L4D is Valve's polished take on the survival-horror genre, and it's a game you shouldn't miss.
Players who stick together and move quickly will likely have the most success in this objective. If your survivor group is always split up, odds are the infected will single you out and pick you off. Some of the most fun I have had playing this game is based around looking for this opportunity while playing as infected. The strategy involved in playing an effective smoker or boomer (infected characters) is something to be admired. Finding the perfect ledge to drag someone over, or a blind corner for a four-way boom is exhilarating, and the fast pace of the game makes your perfect spot only useful for a tiny window of time. Make it count.
While surely my favorite part of the game is playing the infected host to an unassuming survivor party, playing AS a survivor in multiplayer can be a blast, providing that you aren't grouped up with morons. As you near the safe room, health bars start to dwindle, while pills and medpacks are in short supply (although ammo never really seems to be an issue for me, the pistols are limitless). The tank (another infected type) music starts playing, and tensions are on the rise. If you are down to fewer than four members, the infected often try last-ditch attacks to keep you away from the safe room. This is where the game really shines. Trying to reach a barred door with 5% of your health left while being chased by somewhere in the neighborhood of 50 zombies leads to some downright intense action sequences.
While it may not have the depth some newer FPS offer in their campaign mode, and playing for hours on end can drain the enjoyment level, Left for Dead is a high-action, fast paced game that does the survival horror genre justice. Don't miss it.