*Unreal Tournament III*
Though I've never been such a huge fan of the Unreal franchise - mostly because it was waayy too fast for me to handle (*hides in the corner of shame*) - I'm surprised that I've grown to like their most recent game every time I play it. I know Epic tweaked the speed somewhat for the console version, and that is something I certainly appreciate, what with working with a DualShock/Sixaxis controller instead of a keyboard and mouse - though that's another option too.
Single-player is mostly forgettable and is mainly used as a "training ground" for new players, though online co-op is a nice feature. Online MP just totally rocks though, especially in their Warfare/CTF modes. Its epic (pun not intended) in size, and the different vehicles are fun to mess around in too. Simply put, it's torn me away from Call of Duty 4 for more than a week now... and that's an achievement in itself, lol.