BioShock
Considering I already know how it ends - I've seen people play through it on several separate occasions - I am amazed at how immersed I am nevertheless becoming in BioShock. I'm engrossed in the saga of Ryan and Fontaine, and their supporting cast, as revealed in the tapes. And it's striking how much care was taken in environmental design so as to make everything from the architecture to the clutter in each area of Rapture evoke a sense of getting to know the characters.
Of course the gameplay is also fucking fantastic. BioShock has a shitload of gameplay features, from plasmids and tonics to new weapons and upgrades, and they're introduced at a pace just barely slow enough to get to learn one before moving into another - still rapid enough to keep me hotly anticipating the next one. I'm even excited about the Camera!
And what really gets me is the exhiliration of combat. Between the quick-thinking AI (I'm continually impressed by the pathfinding throughout the city), the smart layout of enemy/security locations, and the way every element of combat plays out against one another - fire and oil, electric stuns, armored and unarmored dudes, on and on - even though I'm an avid non-fan of shooters, the shooting in BioShock keeps me coming back.
I'm, what, a third of the way through? The length of BioShock is really commendable, especially given that I'm compelled to spend hours at a time with it whenever I sit down to load my last save file. It's really fucking awesome.
It's easy for a blockbuster game to feel lukewarm if you pick it up after the hype has died down. BioShock still impresses the hell out of me.
Progress: Arcadia