that preview in the end of 2.22 is completely full of discarded material and dropped concepts. Only a fraction of those things actually show up here, so if you're not spoiled yet, you really don't have any idea what's coming in this:

Spoiler Summary from what I've pieced together follows. It's not an exact play by play, because I'm sure a lot of people will do a really detailed version of that elsewhere, but more of an overview with my thoughts on it.

So, the end of 2.22 was in fact the third impact, aborted preemptively by Kaworu. It's not specified, but implied that perhaps without any guidance that third impact would've just been destructive and not a rebirth like Shinji would want. So since Kaworu seems largely to work in Shinji's interest, it seems implied that he stopped it to give Shinji a chance to actually be happy through his actions later. We'll see how that works out ultimately. Oh, and the Eva Kaworu piloted in the end of 2.22 is nowhere to be seen.

Well, the lance in the end of 2.22 results in Unit 01 being stuck in a permanently activated state, with Shinji inside it. They decide to seal off Unit 01 until they know what to do with it since it's now operational, but stationary, and proceed to lock it inside a giant black cross (seriously) and put it into orbit until they're ready.

Turns out they're ready in 14 years.

So we learn quite a few new things in the following minutes as they rip Shinji out and leave him in a hospital gown on the bridge. First is that Eva pilots bodies don't age for whatever reason (fanservice). Second, is that after NERV has been exposed as being an entirely manipulative and corrosive force, even to Ritsuko, Misato and most of the living NERV staff splinter group. Willie, with the sole purpose of exterminating the remnants of NERV. Willie is currently a giant sea armada.

So they bring Shinji back into this splinter group 14 years later, he has no awareness of the passed time yet. Everyone treats him like a pariah and shits on him, and no one explains why. Obviously it's because he wiped out hundreds of thousands by triggering the third impact 14 years ago, but no one ever mentions this at all to him at this point. They also are very gracious hosts, and give him a remote suicide collar that becomes a plot device later. It's sealed by magic lilith runes apparently. This is also important. He also somehow has his tape recorder that Ayanami had. Also a plot point.

So next they fight off a giant sea angel attack from the sea they're on. Misato's new group repurposes Unit 1's AT field as an engine and method of flight for their huge battleship called Wunder. This is kinda cool, but it's it's basically a flying battleship with laser guns that spins. It was neat, but the battle was surprisingly slow paced. So, after the angel is dealt with, with everyone still furious at him and no one telling him what happened to Rei, a replacement Unit 0 shows up (Unit 9) to kidnap him. Shinji hears Rei's voice, and goes with what he thinks is Rei.

So, Shinji gets kidnapped and goes to broken down NERV HQ, and Meets up with Gendo, who now has Seele glasses, and silver Goatee. He tell Shinji to pilot Eva, event though the last thing everyone at Willie told him was not to. Including his escort, Toji's little sister (grown up now. ew, time skip). Kaoru and the Rei clone show up here.

Then follows what feels like a fucking hour of Shinji and Kaoru talking and playing Piano and romancing. It's okay character development, but seriously it moves cripplingly slow, and the set pieces are boring as hell.

In the end, Kaoru shows Shinji the death moon he made in the end of 2.22, and explains his wish to save Rei had a price. But he hopes to use Lilith in Central Dogma to help Shinji recreate things and try again. This would be the Happy End. Hence the title of the film. During this also Shinji talks with clone Rei and feels like shit because she remembers nothing. Then out of the blue Fuyutsuki actually just lays everything on the table for Shinji during a game of Shoji in the dark, about the original Eva project and Shinji's mom, and explains that the Reis are all clones of Yui, who is stuck in the core of Unit 0 and went in without a entry plug. So Shinji connects the dots and gets freaked out and sick for a bit by all the mom-clone-lusting and conflicting info he has about piloting and his death collar and everything. Eva Unit 13 is finished, and he flips out and smashes his tape recorded when he's asked to Pilot it. Kaoru then helps Shinji mellow out by unlocking his suicide collar and putting it on himself. This ends well! : He convinces Shinji that they can try to start over using the power of Lilith somehow.

Expectedly, things don't go swell. Kaworu and Shinji pilot a dual driver Eva Unit 13, that looks just like 1 into Central Dogma to find the Lilith body, and Rei Clone follows them in Orange Unit 09 with a GIANT FUCKIGN SCYTHE. Asuka and Mari show up to stop him, but Unit 13 is hardcore and bats them away, and then Unit 09 and 02 showdown for a bit before Mari in Unit 08 puts it down for a bit. Mari also kinda want's to see what'll happen though so she hangs back. Now, because Gendo is ridiculous, he predicts that Kaworu would take the collar, and thus that Shinji will be alive to remove the lances immobilizing Lilith. Kaworu also gets really bugged out and stops piloting around now because there are two complete lances impaling Lilith, which just shouldn't be. What we're seeing is a result of something else having been at work, and Kaworu doesn't work it out in time. Then for... reasons, Eva Unit 13 merges with Lilith by eating it's red shiney goo, and starts to begin a fourth impact. Misato then appears out of nowhere with the Wunder battleship, and literally hits Unit 13 broadside. Kaworu apparently wanted this to work out differently, but was duped by Gendo, as apparently his getting close to the freed lilith activates the collar, or Misato pressed the button while on Wunder when the collar read blue for Angel. Because, as the audience knows, Kaworu is an angel. Shinji doesn't, or doesn't seem to this time. So Kaoru uses his last bit of control to impale Unit 13 and stop Lilith since shit is just going crazy and Gendo played him like a violin. And then Shinji gets to watch while Kaworu's head explodes 2 feet away while he's trapped inside the fourth impact Eva next to him. The Eva won't shutdown until the plug is ejected, so Mari rips the hell out of his and ejects Shinji. Asuka then stops the infected Unit 09 and Clone Rei from infecting the giant Wunder battleship, which is cool. She goes into beast mode and winds up having to blow up Unit 02 to do it though. This is important for the credits.

With the 4th impact stopped, shit falls to earth, Shinji is at his worst since Rebuild started, quivering in a ball next to his headless friend. Asuka comes and collects him, and they and clone Rei, who is starting to question her existence, walk into the sunset on red sand. Clone Rei picks up the tape recorder that Shinji drops. That THING!

Overall I guess they felt the need to dial it back from 2.22 to give some gravity to the impacts. As awesome as it was to let Shinji man up in the last time, the consequence of bending reality to suit your needs was apparently the utter annihilation of everyone you knew from the Geofront who wasn't part of NERV core. So yea, think Shinji took killing Toji hard before... now he's murdered everyone.

Preview:
 The preview consists entirely of footage of a spliced unit 3 and unit 8. It's just like 45 seconds of Two-face Eva tearing shit up, then diving over an ocean covered by an AT field and talking about the final impact.

Speculation:
 I expect some of the concepts from the preview in 2.22 might have been pushed into 4.X, because it seems like the "Children" might be in a mood to have a heart to heart with someone at the end of this perhaps. Hopefully maybe we can see Shinji get his shit together before it's too late. Again, it seems like Anno couldn't let Shinji be happy in this one at all. He's basically shat on and fucked with the entire film, finding out he's a mass manslaughter-er, and then led into accidentally the fourth impact and blowing up his only friend's head. It's my sincere hope that Shinji winds up being 2x as hard as he was in the end of 2.22 ultimately, but boy did they break him down from that peak in this film. Naturally, this one was so far out there, that you have to try REALLY hard to stick with it, and not think too hard about the inconsistencies.

The Japanese audience I saw it with was FULL of people saying "I don't get it." "It doesn't mean anything." I don't imagine the review for this are going to be as good as they were for 2.22. Overall, I get why they went the direction they did, but 2.22 was immensely more satisfying. I imagine this will hopefully be the outshone by the next.

They seem to be unclear this time on on  the potential for creation each and rebirth the impacts have , and while this can be explained away, it was formerly implied to be  their destruction and recreation were one and the same. Yet Kaworu stops the third impact early despite it being this force for rebirth, only to later encourage Shinji to do something like it again. I suppose it makes sense to stop him if he had no idea what was going on and no one to guide him (ala the End of Eva). But then the fourth impact is started and Kaworu aborts that one as well.  There is some explanation for this in the film, but  most of the exposition on this topic was delivered by Kaworu to himself during a fight scene. I'm sure if I got to hear his dialog there again I might be able to glean a bit more from it, but ultimately it boils down to Gendo being a magnificent bastard somehow and something about the fourth impact being wrong for Kaworu's goal.

My take:
 Kaworu stopped the third impact because Shinji wasn't ready, but proceeded to start the fourth because he was hoping to be the medium for it, like Rei was in previous films. However his Lance was present at the scene and stopped him somehow from doing this, and his reaction somehow triggered the collar before he became the demi-god form he might've.  This makes a lot of his actions make more sense to me, though I'm not sure if it fit what's said there exactly.  I suppose it fits as well with him wanting to guide Shinji through it to keep it from being the batshit insanity of End of Eva all over again.

All of this can be later justified with in-universe religion talk if it's not already, but in the meantime it's just that way because the writers felt like it.

Some chunks of dialog I forgot to mention in my recap that helped piece things together.  The Lances that are supposed to be there are Cassius and Longinus, one for Adam and one for Lilith. But when they arrive there aren't two spears, but two copies of one spear. Kaworu is freaked out by this and starts to sense this isn't right. He also mentions that the spears aren't "theirs" (He/Adam/Lilith), so they're possibly time loop duplicates, or mass production copies made by Gendo. Shinji is so desperate to reset things though that he then proceeds to pilot the dual Eva solo by waking it up red-eye style (he has 100% sync now after the third impact btw), and removes the spears himself. The look exactly like the Lance of Longinus, and Unit 13 releases a second set of hands in order to dual wield the spears. Unit 06 from 2.22 that went berserk was held in the shell of Lilith with these double spears as well, and is absorbed by Unit 13 when he releases it. Next, like the original series Kaworu is the 13th angel, but can't believe he winds up becoming the 13th angel at the last possible moment thanks to Gendo's plan of hiding (infected/virus) Unit 06 there which then "activates" Kaworu. Magnificent Bastard indeed. So Kaworu is thus prevented from helping Shinji through the impact if it continues, and aborts it as I mentioned earlier.

They obviously don't answer all the questions, but at least  Kaworu's reaction and fate should be a bit more clear after this. The lances and the setup are obviously a question that will be addressed in the next movie.

Also final note:  Kaworu reminds Shinji not to give up because there is always hope. This could be really, really important in the next film given how completely wrecked he is by the end of this one.