The immediate difference between the two are the main characters and the campaigns. The new characters and settings have no cross over to the original other than they exist within the same zombie apocalypse. The new characters are not as immediately lovable as the original, but they grow throughout the game. However, the campaigns are pure genius.
L4D1 had fairly mundane campaign settings and outside of one interesting moment on the tarmac at the airport, the game was all about the zombie killing. L4D2, building on epic moments, has included some great show stoppers. One level will have the survivors lighting up a stage at an abandoned rock concert to signal a chopper, while another will have the survivors retreading old paths now flooded by recent storms.
The brilliant part is that its not just the climaxes to the levels. Throughout each, there are a ton of great moments. However, words can not do these campaigns justice. They have to be played to be understood (or for a close runner-up experience for the Dark Carnival campaign, go watch Zombieland).
Also included are new weapons, the obvious additions being melee weapons. After a few hours of L4D2, its hard to think back to a swarming-zombie moment where I didn't have a katana or chainsaw sitting in reserve for that unfortunate moment when my ammo runs out. Sticking with movie references, see Shaun of the Dead for the importance of melee weapons during the zombie apocalypse.
With new campaigns, also comes new gameplay modes. In addition to the classic VS., co-op, and survival, a couple new game modes join the fray:
Scavenge: This is a VS. mode where the survivors have to collect gas cans to fill a generator while the Infected players attempt to stop them. The teams swap each round and the team with the most emptied cans wins.
Realism: This game mode will quickly have players hoping that a real zombie apocalypse doesn't occur anytime soon. There is no returning from death in this mode and everything is hidden from view (no glowing lines pointing out the ammo stack). This mode makes hardcore look carebear.
With the VS. game modes, come new infected, outlined below:
Charger: A hard charging brute that can grab and pound a survivor into the ground. A very much needed "speed" addition to the Infected team.
Jockey: An annoyingly small son of a bitch who can jump onto a survivor and control their movement. There is nothing like walking a survivor out the window of a 30 story building.
Spitter: A much needed, closet-camper punisher, the spitter lays down a pool of acid spittle that damages all survivors in its area of effect. The spitter is what L4D1 needed.
Boomette: A female version of the Boomer from L4D1.
There is no doubt that VS. mode in L4D2 heavily favors the Infected side. Fortunately, this is a good move. It adds bragging rights to finishing a campaign as the survivors and this time around the scoreboard actually feels like a competition. I never paid attention to the VS. score in L4D1, but since almost every L4D2 VS. match comes down to a few points, I constantly keep an eye on my progress trying to run a few more feet when all hope is lost (the farther a team makes it as survivors, the more points they get).
My only complaints with L4D2 so far are outside of the actual game. Some servers seem to suffer horrendous lag, even when they were able to run L4D1 without a hitch. Secondly, the matchmaking doesn't seem to have improved much as many of the games don't fill with players or in the case of VS. games, the sides become lopsided. The fix, as always, is to play with friends.
I plan to spend many hours playing L4D2, probably more than I spent with the original. At some point, I want to see the new infected and weapons integrated fully into the original campaigns and have everything accessible from launching a single version of L4D. I'm ashamed that I even thought about not playing this game. Its fucking awesome.
