Actually... I retake what I said about Fallout 3. It certainly isn't Oblivion with guns (infact, it's MUCH more!)... but it's very short. It's basically like Oblivion in the sense of how much gameplay actually exists. There aren't all too many sidequests, and the main quest is short and ends your game permanently.
The fact you could end quests in different ways is awesome, and is probably one of the biggest things that stands Fallout 3 apart from Oblivion (discounting the setting).
However, there isn't much to do aside from the main quest, and once you do them all, the game sort of... gets old. Similar to Grand Theft Auto, you end up having to find your own way to have fun.
The main quest itself is unique, but doesn't feel grand or epic. In some quests, you even feel as if your just tagging along for the ride, as if the story revolves around everyone except you, which, obviously, isn't fun.
Graphics are ok, but still pale in comparison to the Unreal3Engine and the Crytek 2 Engine.
All in all, unless your a fan of Oblivion, get this. If your a fan of more traditional and in-depth roleplaying, get a BioWare game, like Mass Effect or Knights of the Old Republic.