For me, this was the worst season by far. As abaez said, you really had to suspend your disbelief as there were so many plot holes and liberties taken.
The "worst" season for me was 3. I didn't care for any of the Prado crap. I still liked it overall, though. The show as a whole is just amazing.
Only one cop on top of the sky scraper? Really?
Didn't LaGuerta mention something about spreading her forces too thin? I forget, but I thought she had.
Poor acting this season - I hated both Almos and little Hanks (and his stupid face he makes when he is "serious"). This season doesn't hold a candle to the amazing acting done by Jimmy Smits or Jon Lithegow.
I thought they did great. Olmos had such a small part, but what he did I felt he did great, and Colin's face you mention was really good at conveying how insane he was, yet he didn't think he was. (Lithgow is a god)
Really just didn't enjoy this season and it was very clear that Gellar was in his head and that Deb was going to find out. They could've shortened this season by 2 episodes easily as well.