First two seasons at least.
Season 3, Gene’s stranglehold on the franchise had loosened and it got better from there.
Even so, I agree with the writer whose name is slipping my mind. To paraphrase him, “Gene said, ‘All of Earth’s problems are solved; now go and write drama.’”
Season 3 started getting OK, but season 4 had all those “solo” episodes where we found out the only characters fully fleshed out enough to hold together an entire episode were Pickard and Data. Then 5 started to rev up again, but by 6 the cracks were really starting to show. That sounds like Ron Moore, in various interviews and forums I’ve heard him do about an hour how Gene made TNG impossible.