Awesome storylines, interesting characters, cool action scenes, great plot twists and suspense. Cons: Besides the fact that it's over? Extremely addicting (trust me, more of a con than a pro). And if you're not into thrillers, then this definitely isn't for you!
24 is a mix of suspense and action. I really enjoyed seasons 1-6, but season 7 isn't as great as I hoped it'd be. Cons: Since each season is 24 hours (ok, 17 actual hours w/o commercials), lots of it can become a bit repetitive.