Season 4 is pretty good. The season in general isn't quite as good as S1-3 imo, but at the very least, it's watchable and there are a few episodes that stick out to me as being just as good as the average pre-movie episode (in fact, "Have You Seen That Snail?" is probably on my Top 10 episodes of the whole series)
Season 5 is alright. There aren't many episodes that truly stick out to me, but again, it's at least watchable.
Like a lot of people, I don't like Seasons 6 and 7 that much (although there are some alright episodes) and I haven't seen anything from Season 8 onward aside from Sponge Out of Water. Considering I've heard some positive things about Seasons 9 and 10, I should probably give those seasons a chance.