It felt obligatory that they had to introduce ANOTHER prison so that they can break out. Season 4 was all over the place too but S3 sucked the life out of the show. Terrible considering the 2nd season was my favorite.
I agree w/ HOL that second was the best. The first two are close and so far ahead though that it isn't even funny. Three and four... idk. Both had certain parts that were good, and on a purely episodic basis were not really that bad at all. Just had fairly bad underlying stories and not enough depth relative to the earlier seasons.