Night and day. Oblivion modded is simply put, a different game. Aesthetically it can be greatly improved, but where it shines is in the immersive department. If you like realistic things, there're lots of mods that will make you fell like you're in there. There're mods that have revamped from the stealth system, to combat, to magic and more importantly, levelling and balance between the player and the game.
Oblivion vanilla feels like an average to good RPG. Oblivion modded feels like one hell of an inmersive adventure. Now, prepare to learn some ins and outs abot how to mod it, because there're different levels. Some of them are pretty easy to install, some others need better understanding. However, all the time you may invest, it will be well worth it.
