For it just seems that even though the quests are interesting; they lack what a person would think they'd posses.
For instance: The Independent way. Now you're trying to take New Vegas and shove out both the NCR and Ceaser's Legion without any bad results in a return. So...wheres this? The only main point of this is destroying the leader of the Legion and killing his commander (or not) while for NCR you just kill a general.
Seeing what NCR was like in Fallout 2, that just isn't possible that they wont re-try. I'd add more missions at the end quests to make it really think you are securing your victory when the cards turn up in your favor.
Perhaps get the military on your side and have a coup de'tat of the military leaders that werent there at Hoover Dam to make sure they'd disagree on a military intervention, or bribe a congressman into supporting this new independent Mojave. And then what about the Legion? You kill their leader and his best man; you have to do more then cut the head off of the bull. Maybe ingnite a civil war or have CL literally have the need to go east toward the other cities in order to protect yours.
And then theres a more important issue; what do the locals think? I mean if you were a Freeside local and saw dozens if not hundreds of Secuitrons just parade down there, wouldn't you be a little pissed? Of course; so you'd be wise to also get local support. And by support I don't mean "oh faction is IDOLIZED by me", I mean actual support.
Pledge what you'll do, etc,etc.
Then there's another thing; how do we protray the main factions? We get a weak NCR for starters which really seems to conflict with them taking up whole cities without much trouble. Vault city anyone?
I mean, sure, its clever to put in "the NCR is greedy and wants more land" but to make it military weak because of this rather then militarily aggressive doesn't show us the power they were back in Fallout 2. Then there is a lack of NCR; Regulators and such. All you have is the military, but what of the other viles when a country wants to invade? Usuaully they'd be politicans to make deals, Barons to obtain land (Can't count the ONLY Baron in the ultra-lux, espically when he is the only powerful one), and usually there'd be some inner conflict within the NCR military besides "oh this suxs..."
Then theres another thing someone pointed out; no romance in Fallout DX
Besides the occasional "flirt", in which is kinda cute for a bi version, but then what about the six option in Fallout 2? Where you could actually love someone and bear a child. and I wouldn't mean just 'companions' since you save alot of people and eventually earn a reputation. Make the NPC's more alive.
Thirdly; Deathclaws. When Intelligent Deathclaws werein Fallout 2 and Tactics, those were the best moments. For you have the most fierce beast in the wasteland, talking to you in which is rather cool. Espically since they're very civil in both games. Though we, once again, just get the terrifing Deathclaws whom we just exterminate without any consequences.
Forthly; an actual enviormental change if you kill too much of one animal. Or rather actual raise animals of the waste. You find eggs, which become nothing but decorations. I mean who wouldn't want a pet Deathclaw or a pet cazadore?
Lastly; Lets go back to Fallout 1 "fast travel", where it actually takes time and you face obstacles when going over vast distances of land.