Only season 5 is messy, because Peter McNichol was only in a few episodes. Also they stuck Ally with a Cousin Oliver kid, almost unironically. On the plus side, the kid turned out to be Hayden Panettiere.
Also on the plus side, Jon Bon Jovi was there a lot, and yes he can act, and yes he wore the right jeans for his rockin' ass.
Also parts of season 4 were iffy because Robert Downey Jr. had to leave the show to go to jail one last time before becoming the biggest star on the planet.