I have so many mods on Oblivion (half of them made by me) it can now classify as a FPS, an RPG, Action/Adventure, Platformer, Eroge , and music game. i added graphical updates, maps all around the world, new enemies, quests, weapons, armors, over 300 new races, new cities, A teeny tiny bit of voice acting done by me and friends, and minigames.

Freelancer, I added graphical mods, over 600 new ships, over 1000 new weapons, 87 new systems, a new campaign, and a nyan cat enemy that flys around shooting lasers at you. I also added the last thing to oblivion.

Pokemon Pearl I added new moves and animations.

New Vegas I added a new race.

Skyrim: I added my own version of Esthar from ff8. I had to delete it due to the HUGE lag it caused from being an area almost as big as blackreach with over 300 regular NPC's and a new behemoth enemy that roamed around killing people at random. The only non bland NPC was Laguna, who I fasioned a new weapon for, a staff in the shape of a machine gun that fired repeatedly and had nearly infinite uses.

Megaman battlenetwork: I replaced all the NPC's with cats and all thei lines with meows. It quickly got boring so I trashed it.

FF7 iso: I tried to add a new dungeon but failed miserably.