Left 4 Dead Vs Zombie Master.
This video will be comparing Left 4 dead and a mod called Zombie Master, and how the handling of zombie spawns in both games can show the give and take between consistency and depth, and how these 2 zombie titles released within a year of each other can show this exchange.
Zombie Master is a Half Life 2 mod released in 2007, in this game a group of survivors, typically around 16 accomplish objectives on a map, facing off against waves of zombies and deadly traps in order to try and survive. The main difference between it and Left 4 Dead is the aforementioned Zombie Master. This is a single player who is faced against all the human players, whose objective is to kill everybody. And unlike everyone else who plays it like a first person shooter, they go from a top down perspective, playing it more like an RTS. They have 4 or 5 zombie types, (one is only supported on specific maps), those types are as follows. The Shambler, the traditional slow zombie. This is the cheapest and most common. These can be relatively easily to kill because they're slow have low health and slow attacks. They cost 10 resources. Banshees are fast zombies, that can jump and leap at human players, doing slightly less damage, but their quickness makes them cost 60 per. Hulks are huge and imposing, doing twice as much damage as shamblers, moving faster, and taking a lot more shots to take down. These cost 60 as well. There's drifters, who have a ranged attack that disorients but are relatively weak. They are cost efficient at 25 resources.
Finally there's immolators who cost 100 resources, and explode, but are only available on specific maps. The humans have weapons which are easy to understand, a half life 2 crowbar, pistol and revolver, as well as a generic sledgehammer, shotgun, Mac 11 and Winchester rifle
All this is to say that there's a variety of zombie types, and the expensiveness of non-shamblers makes it difficult to just try and spam a single zombie type just to win. This requires Zombie Masters to try and get an ideal mix of zombies to try and counter both what weapons the humans have equipped, as well as their playstyle. If you notice a specific player really knows his way with a sledgehammer, you might decide to mix in more drifters into your next encounter to kill him off.
Left 4 dead on the other hand, I'll give a briefer explanation of, due to it being a big Valve game with over 11 million in sales. This came in 2008, has a limit of 4 Humans, and has an AI controlling zombie spawns. There is a versus mode, but in this mode zombie spawns are still controlled by an AI so I won't really be getting into it. In this game the 4 human survivors are named, have voiced dialogue and are actually characterized, and levels can be separated into campaigns so there's reason why you're going from one place to another.

To begin, there's a fundamental difference in pacing in combat between the two titles, this is because the default zombie in Left 4 dead is a fast zombie, while in in Zombie Master it's a slow shambling zombie. The reason that Left 4 Dead can get away with this is that the Director in Left 4 Dead WANTS the players to win. When the pressure is getting laid on in Left 4 Dead, the director can give players some kind of break to reload and gain some weapons and health. Zombie Master on the other hand when the players are having a tough time, will lay the pressure on even more, even giving the Zombie Master extra resources when human players die . This gives Left 4 dead map makers more freedom, as the director won’t be exploiting certain events like an elevator dropping into an open area, to kill off all the players. On the other hand, having a human operator can make some maps possible in Zombie Master that would be impossible in Left 4 dead, a key example to me is a map called Tetris, in this map the Zombie Master spawns tetris blocks which can be dropped onto the humans to try and crush them, this is really only possible with a human player, as you can have tactics which are built off of the blocks falling in a specific way to crush human players, which requires some knowledge of the physics engine which can be pretty difficult, or at least cause predictability and specific strategies which can be exploited by players.

Another area where the give and take can be seen is in consistency of experience, in Zombie Master, you never really know the skill level of the Zombie master unless you've played them usually a couple times in the past, and given how there can be 30 player servers, and maps can take 20 minutes, and most of those players have Zombie Master turned on giving them a chance to play, really makes finding consistency between Zombie masters very difficult. When playing Left 4 Dead with friends, you can be confident when you want to play on easy, you're going to have a different experience, but at about the same difficulty level. And after that's too easy, you can go on normal, beat a level at that difficulty, and advance with your same group of friends. Zombie master on the other hand, you can go against a player who's doing it for the first time, or a seasoned veteran who will make you think you never had a chance. This is further pushed by the huge human player count, if there's 16 people on your team, and both your team and the zombie master have a decent shot at winning, that's going to end up with many rounds where you die early on due to some trap  or lucky hit and have to stare and observe other players. That’s one key thing about traps in Zombie Master, they can often be instant death, and whether or not they’re set off is dependant on whether or not the zombie master happens to be paying attention. Left 4 dead lets players re-enter during the map. This kind of inconsistency makes having a major release like this very difficult, because if only 1% of players lose 20 rounds in a row, with 11 million sales that's over a hundred thousand people, and some of those are reviewers that can ruin a metacritic score which can affect whether or not you get a bonus and so on.

Another area  of comparison is how they can use narrative tools, when playing Left 4 dead there's going to be 4 characters even if you're not playing with a full house,  so they can add voice acting and personification to the players. Zombie master on the other hand can have Up to 31 human players depending on the server, so personification of characters can be difficult to impossible, and it doesn't try so you end up with Male_01 instead of Francis. Because of this, Zombie Master can't really have that personification, so it doubles down on player stories to make up for it. This can give Zombie Master more replay value, but also demands more of players skill wise. This makes Left 4 Dead a lot more consumable, as the first or second playthrough of a level will be better because you’re experiencing all the banter for the first time, while the first or second playthrough of a Zombie Master map can prove frustrating as you fall for the traps set within a level. Tonally, Left 4 Dead tends to be more consistent tonally due to the fact every map you end up playing will feature facing off against waves of zombies. Zombie Master on the other hand has a variety of maps which end up having no zombies at all, but I’ll get into that later.

Which gives us another point, and that is Replayability. Both have replayability, but of a different kind. The replayability of Left 4 Dead is built into getting a consistent experience. It’s the type of game where if you and your friends get off of work, you can sit down have a beer play a couple rounds of Left 4 Dead and know what you’re getting into. There’s going to be ups and downs but it gives you and a few friends an experience playing at your post apocalyptic fantasies. And although the narrative becomes irrelevant after a few playthroughs, the Director does a good job of changing it up with special zombie frequency and composition. There can be competitive elements, but less directly so. Zombie Master’s replayability comes from the fact that individual players tend to come up with different ideal zombie compositions that better fit their playstyle. It’s not like traditional RTS games where it goes the ideal amount is 8 shamblers and 2 hulks to kill a group. And the biggest point is that playing Zombie Master can be a rare and rewarding experience, giving you a chance to try totally different gameplay. With friends, this can result in direct competition or competition depending on the round. And unlike most games which can switch this up by placing you on different teams, this doesn’t actually piss you off when you go from being on the same team as a friend to being put on the opposite team.

Finally, a point on maps, Left 4 Dead would have unique voiced dialogue when playing on official maps, that played at specific points. Modded or unofficial maps wouldn’t have that, so you would be able to notice. Zombie Master being a mod without voice acting lacked this difference, but actually was kind of lead to its death due to mapping. I mentioned the map Tetris before, the Zombie Master wiki has this quote in regard to fun maps “These maps are not as lengthy as serious maps and occasionally do not have zombies thus creating a great debate that these should be made for Gmod and not ZM, eventually the 'fun' maps overcome the good ones making the developers disappointed and killing ZM in the end for good.” It lists 26 fun maps, and 3 serious ones. As a mod with a declining audience, modders made maps that appealed to the audience, the fun maps that people played between serious ones, but as they appealed to a wider audience, more and more of those maps were made, and that ended up for lack of a better term “Hijacking” a lot of the audience. People would play on maps where people would micspam, where you’d get killed by “shoop da woop” image macros, and you could ‘roll the dice’ and just instantly break the map. It was light hearted, but was really not what the devs had in mind. There was a sequel, but those numbers dwindled as well, so now it’s hard to actually play these games.

In conclusion, taking away control from the player can give more consistency to players, add more tools for a narrative, as well appeal to a wider audience. Giving more power to the player in this case of controlling spawns, can result in griefing, random difficulty spikes and strange cheese tactics, but even in these situations the gameplay experience is varied, if you have the patience for it that is. And how Zombie Master transitioned can be a cautionary tale of what can happen when appealing to a wider audience, especially if that’s not what you were setting out to do from the start.