Oh yeah, absolutely watch this show. And whatever you do, DO NOT, I cannot tell you enough, DO NOT, DO NOT, DO NOT, read any spoilers. Some pretty crazy twists occur in every seasonthat you will never see coming unless you already know what is going to happen.
Season 1 is slow compared to the others, but still excellent.
It's easy to notice the massive increase in budget Seasons 2 and 3 got, considering the picture not only looks a lot better, but the plots are bigger and there is more violence. Season 2 is one of my favorites and a huge step up from Season 1 (even though S1 was awesome). Season 3 is a season many have a love-hate relationship with. Some love it, some hate it. For me it's a great season but with a few obvious plot holes that really make no sense. Overlook the plot holes and it had the potential to top Season 1 and 2 but didn't because of these plot holes.
Seasons 4, 5, and 6 go together very well in terms of plot. Season4 starts off well, slows down, and then picks up full speed in the second half. It's a lot more violent and faster paced than Season 2 and 3 (at least in the second half it is more fast paced) and Season 5 is my absolute favorite. Starts off with a bang and never loses interest until the shocking ending. Seriously, Season 5 is epic. Don't spoil anything for that season, you will ruin a lot of excitment. Season 6 is a bit of a letdown but is still watchable, even if it doesn't live up to the previous 5 seasons. It's slower paced and the plot isn't as interesting, and on the other end it seems to be a lot more violent.
Season 7 returns the show to the spotlight. It's another awesome season, being my second favorite to season 5. Not as good as 5, but definately amazing stuff throughout the entire show.
Season 8's first 13 or so episodes are pretty much crap. Then during the final 11 episodes things continue to pick up and the final 4 episodes are the most exciting episodes of TV I've ever seen.
So yes, watch 24. The fact that it gets bad later on is true, but it evens it out with just as much, if not more, good. (By the way, don't skip season 6 as it's pretty important to Jack's story, but don't stop watching either, give it time).