#39 - Timesplitters 2 (Kudos to Kupo for guessing this)
For all the steps that multi-player shooters have taken forward this generation, they all seem to be forgetting one crucial thing - local multiplayer. Timesplitters 2 is arguably the best local multiplayer game I have ever played - more enjoyable than Halo 2 or 3; broken out among my friends more often than Mario Kart: Double Dash; better at parties than WarioWare and less "I AM GOING TO SMACK YOU IN THE FACE" frustrating than Mario Party.
With an online mode, the game would've been even higher in my list.
But even offline, splitscreen was just amazingly fun. Virus mode running round the cramped corridors of hospital with nothing but a six-shooter to defend yourself. Playing capture the bag on Ufopia with the sci-fi loadout; complete with sci-fi bots. Running around Ice Station with monkey assistants on trying to best your friend.
God, I lost weeks of my life playing this. And unlike the first Timesplitters, there was actually a pretty hefty and enjoyable single player game to go alongside this which was just the icing on the cake of this incredibly enjoyable package. Again, another one to check out if you still have the Wii; 360 or PS2 lying around.
Oh, and the soundtrack was literally sublime: