I was "immune" to 24 for years but friends finally persuaded me to watch all episodes. So, I did watch all 4 seasons in about 3 weeks time. Having watched all the episodes so close to each other I got a pretty good picture of the show:

Season 1 is very "traditional TV action". It is a so-so season.

Season 2 is the BEST season of all: great action, great political twists. If it was not for the LAME and OFF-TOPIC Kim Bauer sub-plot, it would have been the BEST season of ANY TV series in the *whole decade*.

Season 3 is the worst of all. Especially episodes 1-14 that deal with the Mexican brothers is extremely boring and old-fashioned. Episodes 15 to 24 get a bit better, but not a whole lot.

Season 4 is the second best season of 24. No big gripes as Arnold Vosloo rules the screen!

Season 5 is pretty good too. Not the best and a bit far-fetched, but still good action nonetheless.

One thing that strikes you in that show is that ALL characters are expendable. Characters that you get very accustomed to and have big roles in some seasons end up dead in another season. Except Jack Bauer, don't expect anyone else to survive the 8th season in a few years. Not even his daughter Kim.