Bethesda has marketed this game like no other. Their setup at PAX was pretty spectacular in terms of DESIGN and it's clear they put a great deal of money into making it look like Fallout in terms of art. The game on the other hand is a different story...
I waited in line watching over people's shoulders as they played the game. It's important to note that it was a hacked version (same with EVERY SINGLE VIDEO they're put on the internet). In the full game, there are guards at the Vault exit you have to sneak past/persuade/bribe/kill, you don't have ridiculous amounts of health, you can't find nuclear catapult grenade launchers laying around, basically everything you've seen in every video was faked.
Anyways, everyone ahead of me went on mad killing sprees while I waited patiently noting things I wanted to try out (one guy was in the back reciting Fallout's entire ingame history but I didn't dare ask him if he was an NMA member for fear of being booted off the exhibit). When I got to play the game, Hines meandered over to narrate for me. He tried to "guide" me along the demo... to which I completely ignored him. When I leveled up after leaving the vault, I increased my speech to the max and choose Ladykiller which made his eyebrows raise.
I entered a random house and spoke to Silver, this Jethead who owed Moriarty some caps. With Ladykiller, a couple of new choices popped up and she opened up to me about her addiction. I used my heightened speech to extort her of some caps and decided to check out Moriarty but not before sneaking in her kitchen and stealing random objects like toasters and cutting boards.
Fo3 apparently has a robust invention system as pretty much everything could be picked up. In the 10 minutes I was allotted, I basically wandered around the outskirts of Megaton and entered the town to talk to people; something that NO ONE ELSE DID IN THE ENTIRE BOOTH.
The game's writing is better than what was shown. Some of the characters are downright awful, but other characters are actually pretty funny and well written. I talked to this one old guy who basically went on and on and on about how awesome AMERICA was and we had a long conversation regarding consumerism or something that ended with him fumbling in his speech reminding me of a scene in the original where you talked to a rat and "killed" him by bringing up a paradox in his knowledge.
Outside of the improved dialog, I also noticed that Fallout's world was pretty interesting. The videos don't do it justice, but unlike Oblivion there's actual LEVEL DESIGN. Every building that has an entrance can be entered and the blown out buildings actually have some variety (despite repeat albeit not-really-noticeable damage models). The items and events in the game are randomized and in two playthroughs I noticed varying item placements, mumbling crazies, and merchants.
Other than that... it plays out pretty much like Oblivion. You walk around and do quests. There seems to be more attention to detail, something Oblivion was lacking, and the characters actually having personalities is great but yeah... it's like a total conversion mod for Oblivion.
I'm not going to beat a dead horse by going "NOT FALLOUT URGHFHGHFGH" but I will say that it is a fine game on its own merit. The animations are goofy and the AI varies between decent and downright retarded, but overall it's a decent game and that's all I can ask for these days (well, that's all I expect to receive as I ask for an english release of Mother 3 daily).