Quite simply, seasons past 3 are generally less good. I still like season 4, and seasons 8-9 are at least 30% good, but this show has generally gone down hill with its comedy, increased flanderization, songs, ratings traps, and horrible premises.
Sure, there are gems occasionally. I find myself liking the sandcastles episode, and didn't hate rise and shine, but I think the reason others and I hate it is because it just isn't really good.