I love this game, one of the last FPSes I still play other than Team Fortress 2...unfortunately, like TF2, it's not very playable unless everyone in the round is amenable to being a team player. The multiplayer deathmatch allows one team to take the role of monsters, who have the backing of the zombie horde to make up for lack of guns. Playing it really provides some interesting insights to how the AI effectively functions, by slowly getting the human players to come unglued, either by targeting stragglers or letting the best players get too overconfident and move ahead of the team. Of course, all deathmatch games have this dynamic but it's very explicit in L4D, mostly because it's impossible for one human or monster player to singlehandedly own the opposing team in the way that an ace player can miraculously wipe out a team in Counter-Strike.
edit: The AI controlled human players is extremely competent, maybe the best bot players yet created. But they do show their limitations in multiplayer...among their weaknesses: they're too willing to sacrifice their healthpacks for an injured teammate, and will almost always try to help an incapacitated player no matter how hopeless his/her cause. Real humans can be total assholes, but in some situations its best for the team to leave a straggler behind, especially if the enemy has set up an ambush for the rescuers.
I too have played a lot of L4D. What I find interesting about L4D is the way the game changes dramatically as go up the difficulty levels. On normal difficulty you can just run'n'gun. On expert you'll be knocked down in five hits, so you need to be much more cautious (unless you have amazing reflexes). Manipulating your environment becomes much more important, particularly the use of throwable items redirect the zombies or stop them attacking from all directions.
Tying this back to the article, the L4D bot AI, in my opinion, is intended to just be good enough to get you enough experience to play online reasonably competently. Multiplayer is the real game, and perhaps PvP is the real real game (I haven't played it much.) Bots are pretty poor at tactics, just bunching up by the player. They also don't use throwables at all.
> "The AI controlled human players is extremely competent... But they do show their limitations"
I have often wished that Valve would make the player-bots more explicitly customizable (particularly because I only play team vs environment modes, and occasional really bad bot decisions make the game harder in a not-fun way.)
There are several settings available through the console, but they can only be tweaked if the server has SV_CHEATS on. At one point I had a list of 4 or 5 minor changes that made the bots substantially more competent, the main one being reducing their following distance to about a third of what it previously was. My most wished for change, which I have not been able to find a setting to control, is the threshold at which AIs will use their healthpacks on themselves or actual humans.
I haven't touched L4D since before L4D2 came out, and I hardly played L4D2, but what I found was that the further we got from the original launch, the less people there were on the servers, and the more dedicated those remaining were. It felt like you had to stay very active or get left behind, such was the tactical/practice element.
So while I liked the team-based nature, I found it actually didn't help longevity - for me, at least. Well, more relevantly, this is also the case for my friends - individually I'm a poor data point as L4D was the last game I took any real interest in at all.
The most inexplicable problem with the AI humans is that they absolutely guzzle adrenaline shots. Is there a needle anywhere around? Your adrenaline junkie teammate will grab it and shoot up immediately regardless of the situation. It's a huge waste of a great item. I initially thought it was just a bug, but as it was never fixed, I guess that's what they're meant to do. It's bizarre.
> like TF2, it's not very playable unless everyone in the round is amenable to being a team player
Amen. TF2 and L4D are two games that I consistently play years after the fact which is unlike other games I have.
Unless you're playing with people you know, both games are equally frustrating. Specifically in TF2, it's those who go and play support classes when there are already enough of those in play on the map on your team that makes it frustrating.
TF2 also has a huge accessibility problem which contributes to an overabundance of support class players, but also makes it a brilliant game. As opposed to the Battlefield series, where seeing the enemy first is most of the battle, it's actually difficult to inflict any damage at all in TF2. For instance, I'm at about the 200 hour mark and when I play demo I can only hit ground-based targets with pipes maybe 20-30% of the time - and that's quite good! For beginners, the only playable frontline classes are pyro and heavy. Spy and sniper are also popular because it's easier to survive when playing them, and maybe sneak a few insta-kills. Medic is easy to play, but can be very boring.
tl;dr: Don't hate the player, hate the game. And don't hate the game, because you'd be hating what makes TF2 such a wonderful game to play. Even at professional levels getting an airshot is a remarkable feat.
I want to bring this up because it's a point very often overlooked about why TF2 is a fun game, and that is that it has a reliable and accessible in game VOIP system.
I don't see this talked about much, but it really makes TF2 shine as a straight up fun game. It allows players to communicate in any way they see fit, from the user casual to the highly formal/competitive. That means players can organize themselves to pull weird shenanigans or play very competitively using communication to gain an edge. Also, since voice is such a uniquely human attribute, it humanizes other players who would otherwise be anonymous participants.
The end result of this is that you get highly cohesive communities that make the game great!
Getting an airshot is harder at professional levels because by then they have an extremely good grasp of how to airstrafe - without that they'd be lit up instantly. It's actually easier to hit someone midair in general due to easily predicted trajectories; an easy trick to kill newbie scouts is to wait until they've burned jumps then take them out on the downward arc.
Once you have a lot of practice, it's amazing what you can do in TF2 - e.g. chaining 3 rocket jumps then taking out a sniper while still midair.
Better yet, a lot of mechanics like pyro reflect get much more interesting when you're facing other skilled opponents because of how much prediction is involved in the timing.
edit: The AI controlled human players is extremely competent, maybe the best bot players yet created. But they do show their limitations in multiplayer...among their weaknesses: they're too willing to sacrifice their healthpacks for an injured teammate, and will almost always try to help an incapacitated player no matter how hopeless his/her cause. Real humans can be total assholes, but in some situations its best for the team to leave a straggler behind, especially if the enemy has set up an ambush for the rescuers.