Shane had to die in season 2 but he would have fit in well in season three. Rick and Glen did things(or tried to do things) in season 3 on par with what Shane had previously done, well, except for trying to kill a comrade. Season 2 villianize Shane for doing whatever it took to survive, season 3 portrayed similar actions as acceptable.
I also find it interesting how Hershall sort of turned into Dale version 2.0. I really wonder why they killed off Dale. He was a very important character in the comics for a lot longer.
Darryl has become my favorite character hands down. He took first place very early on in season three.