It didn't just get weird though, season 5 was just ridiculous, and totally pointless!
Imo, season 3 of Fringe is the best TV I have ever watched. All of the characters were on top form, the story was very intriguing, the plot strands were all coming together. It was brilliant!...unfortunately it wasn't getting the ratings)and was moved around a lot) and they felt they had to revamp it for season 4 with a twist that really didn't work(well it looked like it might for a while, but turned out to be a red herring!). Season 4 is still very good though, just a hsame they didn't build on the excellent season 3 a bit more.
Still, I would very highly recommend it