Obsidian's Chris Avellone, who was one of the creators of Fallout 2 and Van Buren, and is now working on Fallout: New Vegas has often been asked about his opinion on Fallout 3. Now he has written about it on his blog.
He writes both about what he disliked in the game:
Didn't like not being able to kill Amata or Andy the Robot at the outset because I hated them both. I didn't like that the first potential companion was a bad karma companion and expensive, but then the twin goals of being an **** and scrounging up a thousand caps became bait and a challenge in trying to get him - when I got Jericho, I felt like I'd earned him as a companion. I think Repair became too valuable as a skill, but it's better than the special case it was in Fallout 1 and 2, so I'd rather that than it remain a broken skill (like Doctor in F2). Maybe because I'm approaching it from the development end, I didn't care, but I think the level cap turned a number of people off, as did not being able to play after and continue the game until Broken Steel came out. Some of the locations I think broke the 4th wall (Dunwich, which I actually enjoyed playing, just not the premise).”
And what he liked about it:
Likes: Opening immersion and re-introducing you into the Fallout world. Fallout 1 and 2 had consistently broken or special case skills that were rectified in F3 (for example, Repair - and Doctor vs. First Aid in Fallout 2 became broken without a time limit, so Medicine was clearly an improvement). Fast Travel. Felt my skills mattered in general. The kitchen bell XP sound. I love radiation more in F3, it makes me pay close attention to the environment, I loved the Grognak text adventure game, I loved the Gutsy and Robobrain combat barkstrings, I liked the usage of the radio and the reactivity to the player's actions - that seemed an elegant way of reinforcing your actions in the world as well as introducing a bad guy you couldn't immediately shoot in the face, I liked a lot of the moments in the game, including suddenly being surrounded by the creepy Andale residents after entering the basement in town, I never thought a neighborhood filled with land mines would be a good adventure locale and I ate my words, loved the juxtaposition of real world mundane locations and their change into dungeons (Campgrounds, Springvale School, Super Duper Mart). Liked tracking down radio transmission signals for rewards.”
For the full thing, go to Chris's blog on Obsidian forum