Hm.
1. Neverwinter Nights 2: Storm of Zehir (reviews are iffy, but I can't resist NWN)
2. Neverwinter Nights 2: Mysteries of Westgate
3. Bioshock (want the CE, but that's impossible to find and horribly expensive, so. . .)
4. Fallout 3
5. The Witcher: Enhanced
Personally, I'm not that excited about Left4Dead, as I don't play multiplayer and I guess I'm probably just burned out on the concept of zombies in games or other media. RA3 is great old-school fun; I'm mostly dividing my gaming time among Titan Quest, Mass Effect, and RA3 right now.
I don't own a console, but even if I did, I'd probably prefer the PC version of COD. 