Skyrim for PS3...
It made my second playthrough much smoother and it did not break my game 80 hours into it. My first save lasted me quite a while (most of the vanilla game and partway into Dawnguard dlc), but I saw the bugs catching up to me and since the patch was not retro active, it was time to start a new character while making different choices.
So I guess it changed the game in a good way for me as I no longer needes to avoid doing certain things in fear of breaking my save file.