Don't listen to the coolaid. I had the same thought and bought the second one. It was bad. You'll be sorry you wasted valuable gaming time on it.
Thats an interesting reply seeing as you haven't necessarily said what you think is wrong with the game.
Its all a matter of taste.
If you only like snazzy graphics, average style humour and writing, sandbox exploration and heads that go boom then stick to Fallout 3.
If you like something a little bit deeper, a REAL RPG, good writting, decent main quests, intelligent/subtle humour, with a much more effective characte system, AND DON'T MIND TURN BASED/ISOMETRIC view, then obviously play both.
To be fair, the only games I have ever played that were isometric and turn based were Fallout and X-Com, and I hated Fallout at first. It was only after getting used to the style of playing that I fell in love with the game and regret not having played them before. It was also my first RPG. I stuck to FPS, RTS and so on back in the day.
So the bottom line is, at least try them. Its not like they are expensive.