Fun competitive multiplayer game. I'm in the closed beta, as a friend who owns a LAN gaming center was kind enough to give me one of his keys.
It looks a lot like Halo 3 with the gravity turned off, but plays a lot better, considering 1) it's on the PC and 2) the controls are nice, tight and responsive (partially because it's on the PC) making for fast, frenetic and fun shooty-gameplay which hearkens back to some of the classic MP FPS's.
Also, just started watching the WTF is... and I was totally thinking a good comparison to Tribes Ascend would be Quake Live and then he said the same thing and I was all "squee".