L4D2 comes by a year after L4D and finishes off what the first one had completely missed (I'm not boycotting in any way)
L4D2 riddles on the same formula. 4 survivors, arcade style shooting through a f***load of hordes of zombies. If you had played the first game you will notice a way more amount of weapons availabe to your disposal, more pistols, submachineguns, shotguns and various rifles (Though you will totally notice there are some lazy similarities between some weapons). The enjoyable will be perhaps the melee weapons. It doesn't really matter whether it makes sense why a crowbar would be in a bedroom of a hotelroom, you'll completely enjoy the gore you'll be able to inflict with guitars, baseball bats, swords etc.
Speaking of gore, you'll notice L4D2 spices up the blood a bit from the first one. You'll recall the comical splashy blood from L4D, now is upgraded to a juicy level. Weapons will get stained by the crimson liquid, severed limbs will fly in all directions. The ground will be splattered with brains and blood after killing a horde. It makes it more enjoyable for the experience of onslaughting every foolish horde that comes by and charge at you.
Zombies are now more lively. There are more character models and they seem more fitting than the previous one (They wear shorts, they wear more casaul clothing). You can shoot off limbs and they can still charge at you in a mad frenzy, spicing up things.....You will also encounter law enforcement zombies, who wear armour and can take a few more hits. Aside from normal zombies, there are also 3 new more infected. Compared to the boomer, hunter and smoker from the last game, this time the Jockey, Charger and spitter have a more obvious uniqueness to themselves (Seriously? when l4d was released I totally expected the hunter and boomer before any details were anounced. Talk about cheesiness). The Jockey can hop on people and drive them around (You will recall hunter bunny hopping style with this infected), the Charger that charges at people at whacks people, the spitter can spit acid and seperate survivors and inflict dmg. These infected work magically when in teamwork as usual. And you will find a lot to discover between combinations and traits.
But on the other hand, the survivors AI continues to be disappointing. Though the series was never intended for singleplayer, the AI still strucks at a very disappointing level. They continue to get stuck in terrain, loves to walk into spitter puddles or let boomer vomit upon themselves. Their reaction towards special infected is pretty much abysmal, as they still prefer charging at you (And getting stuck in the walls for a few seconds) and start whacking at the special infected (Or charge up next to you and shoot the infected). By the time they save you usually you will have lost half a life. But that's not really an issue.
The maps are pretty well designed this time. You will notice quite a lot of areas to explore compared to L4D's close and concentrated space (No, having 10 office rooms to explore is not what I call "Open ended"). You will find huge corridors and lobbies to run around and loot weapons (There are a s***load of weapons lying around this time) and navigate through maze like maps. And also you will notice there aren't as much illogically placed debris to be made as an obstacle.
The game modes are pretty much the same. Campaign, versus, survival. The added modes are scavenge, where basically survival+versus at the same time (WOW VERY INSPIRATIONAL *cough*), and a realism mode (Which basically puts u in expert difficulty.....-.-). Don't expect much originalty on this category, but they all remain very enjoyable provided you have an excellent team that co-operates well.
The sounds of this game is pretty much the same. The gun sounds have been recycled a bit, though everything works fine. The dialogue between characters have improved vastly, as each character displays their own personality in their own way (They will mock in different ways too). Compared to the first group of survivors, you will feel more color into each of them and they seem more closely connected to each other.
Lastly the graphics are pretty much standard. The gore is pretty awsome and everything will be splattered into a mess. The lighting and textures are excellent, though personally I say they don't stand out or evolved epicly in any formidable way.
Overall, L4D2 fixes everything L4D had missed that I wanted. The gore, the infected, the weapons, the map design. It makes me feel L4D was a cheap demo of it, though I FULLY RECOMMEND BUYING THIS GAME AND NOT BOYCOTTING IT. So what are you waiting for? Drop the first game and get this game now to enjoy the zombie apocalypse to it's full potential