Bethesda is very capable of creating a decent first person RPG. Daggerfall and Morrowind are good examples. Unfortunately they opted for more of an action game approach with Oblivion and Fallout 3. I think one of the big problems Bethesda has always struggled with is that they are incapable of creating games with good and diverse detail because they try to cram in too much content, and most (if not all) of it ends up coming out mediocre at best. Even Morrowind (which I consider Bethesda's best game) came across as bland and lifeless most of the time with uninspired quests, interactions and dungeons. Oblivion and Fallout 3 are no different.
The writing in Fallout 3 is an obvious improvement over Oblivion at the very least, but it's also little more than a mashing together of previous plots in the series. Even with the "advantage" of using other people's work Bethesda still managed to litter the game with plot holes, inconsistencies, and illogical design decisions. I'm not even going to mention the oft horrendous dialogue. Fallout 3 is okay for what it is, but it's a horrible sequel and I can't help but feel that Bethesda is incompetent every time I play it due to its banal world and quest design, and uncreative, lackluster writing.