Yeah, I think that was a complaint of some critics/fans during s4. Didn't bother me though. It made for an awesome end to the season with him coming out on top. Yeah, 5 is kinda hard to rank yet, but I mean, I've really enjoyed every episode thus far, and I'm 99 percent sure I'll enjoy the rest of the episodes (unless god forbid they start sucking).
I've watched 'em all in preparation of s5. The last few weeks or so leading up to the s5 premiere all I did was watch anything relating to Breaking Bad; episodes, those inside things, etc. Yeah, I hope if he does quit they'll still have use for him; Mike's an awesome character