If not, there's a "lite" version on the App Store which will take you through the game's first few "hours" (in reality, just a few minutes per segment) of stages. The game itself features Jack Bauer backed up by Chloe doing what else but saving Los Angeles from various terrorist threats. The grid-based action gameplay is simple but fun, and the shooter stages are broken up with encryption and driving minigames. None of it is brilliant, but just like the show, watching Jack Bauer kill bad guys is usually good enough.
It's too bad they didn't do more -- 24's strengths have always been in its breakneck story pace and twists and turns, and just from playing the first few hours in the lite version, this seems like a Jack-and-Chloe story only (Bill appears in a suit on the menu screen, so apparently he shows up later, in some role at old CTU). If there are any cool story twists or turns, they take place more than four hours in -- it would be great to see Michelle or even Nina (if this is before Day 3) again, but I doubt we get that. Still, it's got Jack killing and blowing stuff up, and that's never a bad thing.