It's going to have to be pretty *bleep*ing awesome to beat Bioshock in my book.

I think the only reason someone wouldn't like Bioshock is because they are a hardcore shooter fan and the RPG elements turn them off a bit. While the Half-Life series is innovative in many ways, I would argue that the ambience in Bioshock bests it in the single-player department. Obviously Half-Life gets bonus points for possessing several multiplayer mods that are fantastic and deep, especially with Team Fortress 2 packaged into The Orange Box, but I can honestly say that I've yet to play a shooter that is anything like Bioshock.

I've played System Shock and System Shock 2. Personally, it annoyed me that the weapons degraded to shit after two shots, I'm glad they took that element out of Bioshock and made it less of a pain-in-the-ass to find ammo. I started Bioshock on Hard and am still not completely done with it yet after three or four weeks (of course, Halo 3 has something to do with that) and I find the story to be possibly the most compelling I've seen in a video game, let alone a first person shooter. I also enjoy Citizen Kane and other types of dystopia literature though, so that could be part of it.