Adult player? Not much time for gaming? Gears of War is an excellent choice.
Gears of War makes a perfect game for that reason: it doesn't take long to jump right back into the action, and it's light enough on story that you can get the game going without worrying that you've forgotten something. Each step along the way in single player mode is basically a firefight. The boss fights are relatively self-explanatory - they're just tough - a fact that I believe is a real accomplishment since most boss fights consist of figure out the weakness and that's about it.
If you're looking for something exciting and entertaining that you can put down and come back to several times, this is an excellent choice.