Every site/podcast out there chooses theirs, so I thought I should, too. I'm going to limit this to 2008 games that I actually played in 2008, as opposed to older games I played in 2008 or 2008 games I haven't played yet. You have to draw the line somewhere.
I don't think I ever named a game for 2007, though, so here's that one first: BioShock. Honorable Mention goes to Halo 3.
Without further ado, my game of the year 2008 is: Metal Gear Solid 4. It was completely awesome, and as good a cap to the series and wish fulfillment as could be hoped for. Who could forget Metal Gear on Metal Gear battle, or Snake's agonizing crawl through that microwave tunnel? Unbelievable, I loved it. Pretty good control scheme, even!
Honorable Mention goes to Gears of War 2.
I didn't actually play that many 2008 games in 2008...