I thought it remained pretty strong through Season 13 (the finale of that year, Poppa's Got A Brand New Badge, I still remember very fondly).
Since then it's produced good stuff, but it's pretty inconsistent.
I'm basically the same, but 12 is a lot stronger than 13 for me. I used to think 9 or 10 were the last good years, but 12 and 13 both have quite a few good episodes. (And 14 is full of stinkers.) Maybe they look better in retrospect compared to some of the later seasons?