The successor to Left 4 Dead, this second game adds new maps, new weapons, new special infected with new attacks and even new characters. But in many ways the most important different between the two games is the scoring system.
Without mods, the first games scoring system really did tend to induce rage. A single mistake on a map and you could lose so many points that teams would be totally demoralized and either fall apart (making the game effectively over) or just quit (making it absolutely over). For hardcore players this was half the fun, but for the average casual player it could make Left 4 Dead a little too frustrating.
Left 4 Dead 2 on the other hand had a far more forgiving score system allowing teams who fail badly on map 1 to still feel they have a good chance of clawing the in back in the next 3 or 4 maps. With party wipes being a little less likely due to the removal of the quad cap, Left 4 Dead 2 is still a game people can play causally and still enjoy. With the extra variety of a lot more special infected meaning a lot more variety in possible tactics, Left 4 Dead 2 is still one of the best team focused games that I have ever played.
If you have a small group of close friends who love winning through superior team work rather than superior twitch skills, Left 4 Dead 2 is one of the best PvP games you could try. But be warned, playing with random people you have never met can be rewarding, but more often than not it can be bloody annoying.
HOURS ON RECORD : I don't play this game on my public account. I have over 1500 my private account.