There are a handful of exceptions, but there aren't usually many First Person Shooters that I look forward to. Far Cry 2 is high on my list, but I'd be hard pressed to name even 3. Shooters are just so generic these days... A game would have to feature something really out of the ordinary to appeal to me.
I have (only) recently started playing Bioshock. That game was always high on my list but I never managed to find the time to play it. Now that I finally am, I know that I had good reason to have it on my list; Great gameplay and -above all- a fantastic story, superbly told and in a unique setting.
I have yet to determine why Left 4 Dead is high on my list. It doesn't seem to be doing anything that hasn't been done before, but somehow it has been on my radar for nearly a year now. The below trailer is one of many that have been made available. Enjoy, and perhaps after watching it, someone can tell me why I've got it on my radar. :)