Not all players liked Fallout 3. Some criticized it for being a first/third-person shooter (previously, the franchise made isometric RPGs), and some for not very high-quality shooting.
According to dissatisfied users, Fallout 3 is just "Oblivion with guns." Recently, in a conversation with Game Informer, Todd Howard actually confirmed that this is the case.
The team was heavily influenced by the success of The Elder Scrolls IV, and gamers expected to see something in the spirit of Oblivion:
[...] the "Oblivion-ness" of Fallout 3, if I may say so, is largely due to the fact that this game became our next step after Oblivion. We were essentially rebooting the Fallout franchise, which people hadn't seen for a long time — in a completely new format. But at the same time, we were releasing [Fallout 3] after Oblivion, which was a huge hit, which means we had an audience that expected to see something from both series at the same time.
Todd Howard also explained why Bethesda games have a camera switch between first/third person view:
What we like most about games is the ability to put the player in the world. I think doing it in first person, and then optionally switching to third person, is the best way, because it feels like you can reach out and touch the world around you. Making something believable and alive in this format, in my opinion, is still the best way to show a virtual world — and that's essentially the main thing in our projects.