oblivion is way better theres magic , level ups , create your own character , make your own class and most of all cause as much mayhem you want! (PS even though GTA IV has the internet its just the same stupid people and you can't talk to anyone you want. And one major thing is you don't get side mission...... well you do but not much!)
GTA 4 just didnt live to what I hoped it would..I expected an upgraded version of GTA san andreas
I found GTA 4 to have better character interaction...Better graphics and better fighting. However it didnt have side missions much and it was a lil on the short side
Oblivion is packed full of awesomeness...No need to explain it but it is just that awesome
Oblivion is so much incredibly better, because it has the awesome storyline, and an entire world to roam in doing whatever you want. you have tons of choices to make, and it also has a ton of official mods, and also player made mods.
I thought GTA IV was a huge letdown. It was a good game, but it just didnt live up to expectations. I enjoyed Saints Row 2 a thousand times better for some reason.
Oblivion was very good. One of the best on the 360.