I think he essentially got corrupted by power, despite looking a "good guy" in TNG. He probably was, but then he changed due to holding command of the Council.
Gowron was never portrayed this way in TNG. Re-watch "Redemption" in which the character was introduced. Everybody considered him capable of poisoning K'mpec.
From the very start, Gowron was always portrayed as the lesser evil compared to the Duras family. He was a son of bitch, but at least he was "our" son of a bitch.
This is true I guess. I remember in Reunion he tried to bribe K'helyr.
I've always wondered what Picard have said when he heard Worf of all people killed Gowron. Most likely as a long-standing Captain, Starfleet would have given him the heads-up on all that Sisko and co. were doing, and probably said good riddance to Gowron and "yay!" for his former Security/Tactical chief killing him.