The Unofficial Patch is not really a mod, but while the default basic patch fixes multiple bugs and restores only little unused content that has no impact on gameplay, the optional plus enhancements add further improvements and restore a lot of hidden content, including new quests and new maps!
Get it as usual from The Patches Scrolls, linked under Official Page in the right side menu.
Posted by TheUnbeholden on Oct 25th, 2013
+Recreated missing Hallowbrook atrium level, thanks to EntenSchreck.
+Moved Sabbat choice into Hallowbrook atrium and added missing XPs.
+Restored male blood doll at Red Dragon by using former Tong mugger.
+Recreated "maze" room at Grout's Mansion and restored three icons.
+Fixed some minor discipline issues and restored the basic versions.
+Restored ten decals, moved others and removed restored from basic.
+Fixed warform using occult items issue and improved Bloodheal rate.
+Added two inspections, warehouse boss talk trigger and moved Yugo.
+Increased flamethrower ammo and provided Desert Eagle ammo earlier.
+Disarmed Dominated guard bomb on taking and fixed one sound there.
+Avoided crashing when testing out too many histories, thanks to AJ.
+Added Intimidating Milligan for Nosferatu and fixed armor effects.
+Made it possible to give redundant items to LaCroix and other NPCs.
+Unleaked and improved library and atrium maps, thanks to Psycho-A.
+Restored discipline or weapon selection toggle and Flynn as vendor.
+Moved crying girl near cops at pier and changed her to unique NPC.
+Restored Ocean House boiler model and animated warehouse generator.
+Fixed details of thug, Andrei, Ox, LaCroix, VV and Lily dialogues.
+Made spooky cover sound once and plus only and added steam to Yugo.
+Removed thugs from diner after quest if you avoided fighting them.
+Fixed warrens mist issue and made fatguys use the claws more often.
+Restored or fixed fourty NPC gestures and fixed Confession blocks.
+Made Braid Talisman raise Wits and restored SM Chunk avoiding rain.
+Added Empire Hotel and ending dance spots and made Glaze one plus.
Fixed two particles, a door and added loading tips texts to Extras.
Restored three skyboxes to warehouse, Dane and Hallowbrook atrium.
Corrected Grout's mansion decals, tutorial bucket and tattoo boxes.
Fixed croucher laughs and no floats for females bug, thanks to AJ.
Updated SweetFX to 1.5 and included a preset, thanks to eeekitties.
Fixed pause messages in engine.dll, random sounds and many floats.
Added widescreen resolution support to engine.dll, thanks to Behar.
Repaired many sound files with broken looping, thanks to Psycho-A.
Improved installer by providing additional choices on installation.
Added Bloodlines SDK to Extras folder, thanks Psycho-A and Fire64.
Corrected three interesting places with wrong bum animations in SM.