When B5 first started, I had G'Kar pinned as a bag guy - didn't like him at all. With Delenn it was hard to tell, although after "And the Sky Full of Stars", it looked pretty much as if she were one of the baddies, too - she was certainly up to something! Londo, I felt sorry for. Ivanova, I figured out around about "Eyes" that she had to be a telepath herself.
When the second season started, Sinclair left and Sheridan came aboard, I was thinking "uh-oh! Delenn's Gray Council - she ain't gonna be happy that the Starkiller is running things on B5! There's gonna be fur flying, lots of fireworks, and huge knockdown, dragout fights!" Boy, was I wrong!
Then G'Kar starts becoming, if not likable, then sympathetic, Londo, I started disliking intensely. Delenn was still obviously up to something - but it was becoming clearer that she was one of the good guys.
Lennier? That definitely was a surprise, and I'm still not entirely comfortable with the way his story ended - it just seemed so out of character. Okay, people do sometimes behave out of character in extreme moments of stress, but even so.....