I thought season 3 was a bit weak, myself, I liked Jimmy Smits and I thought he played a good character but there were parts that I didn't like, for example, The Skinner, I know they have to have a big bad in the season but by the end of it I was so into Jimmy Smits and the way his character was going that I couldn't care less about The Skinner anymore - he shouldn't have been the big finale kill. I found a few times that that season seemed to treat the audience as if it was a bit stupid (especially all the scenes concerning LaGuerta trying to figure out if Prado was linked with Ellen's murder). Also that they kept bringing up f***ing Freebo all the way through the season - I don't care.
I make it sound like I hated the season, I didn't, I really enjoyed it but there were just some really weak moments in it for me. Season 4 was an amazing improvement.