I don't think the deal with Shane was bad. It was good, and one way to tell the story. However, I was a fan of Shane and his actor and if I could alter the story, he would have gone away from the group some time during the season, being able to return some time in a future season as either an ally or an eventual bad guy. Would be a cool thing to do, just like with Merle (Though I doubt Merle would appear as an ally)
I did agree with many of Shane's decisions. The only problem with Shane was his instability and I actually thought it was slowly starting to work out after the episode where they were to leave blindfolded Randall. I guess in that scene where Lori in ep12 actually didn't show her despise to Shane his obsession with her got worse and he was confused and simply stopped caring. I think even if the thought of killing Rick had crossed his mind and in season 1 he somehow tried to get the feel how it would feel while aiming at Rick, he wasn't planning to do it and didn't want it (only subconsiously) except for in the very latest time.
Like many seem to believe, Shane was not a complete monster though. He did love Lori, Carl and showed empathy to Carol, seemed to like Andrea, even starting to loose his tension with Dale. He was jealous, broken, and needed to either get away from Lori for a while or well, what happened in the last episode was gonna be bound to happen.
Next episode will be filled with lots of action and while I thought the farm would be overrun much earlier in the season, at least it's finally gonna happen and it's gonna be pretty nice I think.