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.
With this mod you basically get a game that is 300% better than it was on release without sacrificing the original feel of the game. The passionate and professional author known as Wesp and his many contributors certainly deserve the "Leyends" status they have gained among the many Vampire fan circles.