The Unofficial Patch is not really a mod, but while the default basic patch only fixes bugs, the optional plus patch restores a lot of hidden content, including new quests and new maps!
I couldn't even play the game before I downloaded this for some reason, but now it works completely! I also love all of the features. It adds much more depth to the game, such as deciding what your character's history was. 10/10 because it deserves it! Keep it up, man!
Really made the game playable, though now there are better alternatives. I would recommend the Camarilla edition, which adds much needed replayability value to the base game without tinkering with it too much and destroying the atmosphere. A great balance I would say.
If for some reason you don't like that mod, then the unofficial patch solo is for you.