Season two was the worst season of The Wire IMO.
The Shield side-stories sucked. Dutchboy, Claudette and all their side cases were boring. The Strike Team and the main plot were awesome, but the side plots is the only reason that show isn't on my top list.
Edit: Actually I just remembered (SERIOUS SPOILER, if you haven't watched all of The Wire DO NOT LOOK JERKFACE) McNulty jumps the shark so hard in season five that it does really ruin that season. Forgot about that. I did like the ending / message / social impact of the whole series at the end of season 5.