I liked Fallout very much, since it remedied many of Oblivion`s downsides. Plus, it had an excellent atmosphere. However, unlike Oblivion, Fallout had no parts which particularly stuck to mind. There were no particularly briliant quests like with Oblivion (such as those of the Dark Brotherhood). Also, Fallout had less freedom of choice since, unlike with Oblivion, there was not much to do outside the main questline.
Overall, I enjoyed Fallout 3. However, it certainly does have room for improvement.