I shared some of the concerns expressed both here and in youtube comments when I saw that video originally. Playing the game afterwards, my opinion changed a fair bit.

Carn is playing really well in that video. It's not the walk in the park he makes it look to be. I got crushed by crushers, I fell into slime, I ate arcturan plasma, and even spiders gnawed my feet to death an embarrassing number of times. The difficulty seems roughly on par with your average modern Doom PWAD, perhaps even slightly higher, and those are the very first levels. For more competitive players, there's always the speedrunning and score modes.

Level design, monster behavior, eyecandy... All I know is when you've got the game in your hands, it's a blast to play. The player movement feels beautifully right. It runs smooth on your average midrange gaming computer from a few years ago, and (obviously IMHO there, but I stand by this) it looks gorgeous in action. The weapon feel is great, I could just run for hours blasting stuff with that shotgun.

Honestly, yesterday I started up a Doom wad right after playing Wrack, and it felt wrong - strictly speaking about the player character. Not a diss on Doom, it's just the movement in Wrack is really, really fluid and enjoyable, reactive, even the jumping feels good (ask me how I [usually] feel about jumping in first-person shooters).

This isn't to dismiss other people's concerns, of course; it's just I believe the core gameplay, the meat of the game is already solid. Is there flaws? Could it be better? I don't know, I'm too busy having fun; and I think once you've got that fun part down, once you've got something that is engaging enough for people to want to play and replay it and have more of it as soon as they get a taste, every other aspect can be improved if needed. Level design in particular is something people might be able to tackle themselves, as the editor seems like it might be easy to use (for anyone who isn't tragically tech-inept such as myself, anyway).

I could go on and on about how much I like this game, but really I'm not looking to convince anyone my opinion is right as much as say this is well worth keeping an eye on and an open mind about. I was fairly negative about Wrack early on, previous topics should be proof of that, and a mere one week ago still had the thought this might be something good but that likely wouldn't appeal to me personally, and yet did a complete 180° within the first minutes of sitting down and playing the game. Now? I find myself considering moving on from Doom to Wrack, as the main FPS I'd mod and play.