Videogames are for nerds and losers
Most mods simply add in new locations, adjust features, and add some more content to a game. Rarely they are an entire expansion that is as large as the base game itself, with a whole new interesting main questline and countless others. Nehrim: At Fate's Edge not only does this but removes level scaling, adds in new enemies, ramps up the difficulty, and creates a world with a great attention to detail and variety.
It's a must-download for anyone who's tired of default Oblivion.