The Unofficial Patch is a combination of the default Basic Patch which mostly fixes bugs only, and the optional Plus Patch, which is kind of a mod adding various tweaks and implementing a lot of unused content, including new quests, levels, weapons, items, characters, dialogue, graphics, models, sounds and original music! Included are also the optional Patch Extras which feature Player Mods, like shaders suites, as well as Developer Tools, like the Unofficial SDK to mod the game.
A complete must-have; thanks to this unnoficial patch, you can have the whole game (almost) free from the most fatal bugs plus it also restores the cut content which never made to the vanilla game.
You want more replayability?. Try this out!.