Exploration was lame. The city of New Vegas was a let down. BoS were disappointing. And the beginning of the main quest line is long and boring.
Oh and as zodaex said, Steam, complicated things more than it should have. So please exclude it next time. They made getting the veteran armor practically impossible for an NCR fan.
Spoiler Battle at Hoover Dam was... well alittle of let down. Less a battle more of a skirmish.
Lack of interesting settlements. Search Light disappointed me to many lengths. Lack of NCR v Legion skirmishes. Camp McCarren inside was dark as hell. I kinda hate how Rex is part robot, makes it less able to bond with him via RP. hardcoe was more of a burden than challenging. Companions go unconscious rather than die, that was stupid, which kinda forced me to play hardcoe which is why it pisses me off. New Vegas being divided by giant gates into little sections (what were the thinking?). Loading screens got way to repetitive. Casinos were too, empty. Come Fly With Me is the worst quest in the world after playing it two or more times. Creating new characters seemed like a burden to me, rather than a chance to try something else. It seemed like all the fighting happened AFTER you start playing. Most of the quests seemed to go on, back and forth, Venture! and Come Fly with Me were extremely notable for this. Seemed like all the cool stuff was happening out of the player's reach. The wasteland sure lived up to its name this time, here is something cool,
after an hour of walking oh here is something else cool. There were a bunch of pointless locations, like the Devs wanted to fill in the empty space of nothing and dust with a shack or two. They made getting a "player home", a burden. Invisible walls everywhere you turn got really repetitive: "Hey I think I might climb this short hill
Bumps into air, damn well I guess I half to drag my ass for half a mile til I can find a path that leads up to the top of this, oh wait the enemy controls it, kinda defeats the purpose of going up there now." You could never really "join" the factions the game proposed, and even if you did, they made you this Spec Op beast who magically wins the war for them, permitting you can even call what was going on a war, seemed like the real war happened before you got shot. People call FO3 a sandbox, well this game really is a sandbox. They basically made it so you could talk your way to wining the game. The military was everywhere, I can accept this IF THEY DID ANYTHING. Novac was disappointing.
Spoiler Nelson looked like it would be a cool settlement, if it wasn't burned to the ground. Which brings me back to my point where all the cool [censored] happened before you could even physically play the game.
the Lucky 38, probably the coolest casino every, lacked people, wow. Creating your character's face svcked. Your character looked the complete opposite of what you made.