New Vegas is viewed by some as "the real Fallout 3" since much of the talent behind the first two games finally returns. It uses the same Gamebryo engine that Fallout 3 did, however, so if the core gameplay didn't do it for you there, very little has changed.
There are a bunch of little tweaks that caused me to enjoy this one a bit more than Fallout 3, though. It returns to the West, which is really where Fallout works best (from the Wasteland beginning the series has really been a kind of post-nuclear Western). Though I think it might actually be geographically a bit smaller than Fallout 3's map, there's more of a diversity of terrain (everything from red rock canyons to snowy forested peaks) and the map is absolutely crammed with locations and things to do. In contrast to Fallout 3, which had a lot of dead copy-pasteish space, and also kind of felt like only half a game requiring you to buy DLC to get the other half.
There's a more robust licensed soundtrack for the game's radio stations, a mix of country-western ballads and Rat Pack swing and crooning that suits the environs very well. I could have done without the immensely overplayed Ain't That A Kick In The Head as the game's de facto theme song, and it probably cost as much to license it as it did every other song combined, but I guess a Vegas game has some sort of contractual obligation to include it. Fortunately it also introduces you to a number of nice obscurities, such as gunfight balladeer Marty Robbins' Big Iron
, Tony Marcus' Lone Star
and Heartaches By The Number
by Guy Mitchell. Oh, and Wayne Newton is a radio DJ.
There's a Hardcore mode, which I didn't bother with, but is a nice touch that I'm sure a number of fans have been looking for since the series began - it forces you to account for hunger, thirst and sleep among all your other problems, and all items have weight (like ammo, which doesn't in the regular game). There's also some level-scaling enemies, but not as many - in fact, one major plot point at the outset is that you can see New Vegas just to the north from a hilltop in the starting town, but actually trying to walk directly north will get your ass handed to you by Deathclaws, who start out immensely more powerful than you and stay that way until close to the end of the game.
Finally, in the (rather long) list of things NV does better, is the implementation of a faction system akin to that of Fallout 2. It's more robust than the karma system of Fallout 3, as individual factions can view you as good, bad or a variety of places in between depending on how you solve quests and how often you shoot their members in the face. Actually seeking out and improving relations with the individual factions in side-quests also comes back to serve a tangible purpose in the endgame, where you can either enlist their aid in a gigantic final battle, or just convince them to stay out of it entirely.
Oops, I did forget one last thing, but it's related to the factions. NV does "moral greyness" and "player agency" a bit better than Fallout 3 did. You were free to nuke towns and be a giant dick in a number of ways in Fallout 3 ... but the consequences were largely relegated to Optional Sidequest World and didn't really have much of a bearing on the main story and eventual endgame. No matter what atrocities you chose to commit, the main plot still hummed along merrily whenever you chose to get around to it, and the endgame options basically boiled down to either "bring fresh water to everyone" or "bring fresh water to everyone but also genocide the muties while you're at it". Almost everything you do in NV, sidequests and otherwise, has a bearing on the eventual climax of the game.
As the story begins, you're a nameless courier tasked to deliver a mysterious platinum poker chip to the reclusive leader of New Vegas. You're ambushed and left for dead, and initially your only goal is "find and murder asshole who shot you in the head." But en route to locating said asshole, you'll slowly become embroiled in the region's great conflict - the NCR, settlers of California and closest thing to a legitimate democratic government that the Fallout world has, versus Ceasar's Legion, an army of slavers who have taken over Colorado and Arizona and are intent on pushing all the way west. Meanwhile, New Vegas and the Mojave *were* independent before either of these dickknockers arrived, and there's other factions that would like to keep it that way. You're free to align with any of these forces, including the rapacious Legion, or try and find a way to claim New Vegas for yourself. Initially, things seem pretty clear-cut - while there are some issues with the NCR annexing independent territories without caring much about what the present residents think, they seem exceptionally benign next to the prospect of being overrun by a mob of rapist slavers. If you choose to ally yourself with them for the endgame stretch, though, you'll see much more of their ugly side - they basically want you to either assassinate the leaders of or just entirely genocide any faction that's even mildly inconvenient to them. It still doesn't have quite the subtlety and "difficulty of predicting the least harmful choice from among a bunch of shitty options" quality of the Witcher games or Alpha Protocol, but it really ain't bad.
New Vegas was actually flirting with a 5, but in the end I felt there were just a few too many technical issues. The worst one is simply glitchiness - Fallout 2 was mysteriously way less stable than the first Fallout despite using the same engine, and that same trend somehow continues here. There's not just one common bug that will prevent you from even getting past the introduction this time out, there's a whole RAFT of them, which vary depending on what your specs are and even what brand of computer you have (for example, there's a bug that causes Lenovo's auto-restore system to crash the game out after the title screen). If you're playing the latest version off Steam or have the most up-to-date patches for the boxed retail version, it's now much better than it was at release once in-game, but there's still the occasional mysterious crash to Windows, mysterious jittery slowdown for no apparent reason, mysterious freeze-ups while loading saves, enemies spawning or running into areas they shouldn't be and killing key characters, companions not following you or not following your orders, quest objectives bugging up, and so forth. Quest markers can also be really obnoxious when they're on/near mountains or indoors in an area with lots of stairs and multiple levels, as the map doesn't really help much in these situations. In general there was a bit too much time wasted just needlessly walking about vast environs looking for event triggers.
In the end, New Vegas isn't so much the "true" Fallout 3 as envisioned by the original Interplay team as it is their best effort at cramming such a game into the confines of a stock Bethesda action-RPG. While it isn't the BEST thing we could have gotten, it's not a bad thing at all, and it does make a number of improvements over Fallout 3 and lends some hope that the design of Fallout 4 will be more responsive to what longtime fans of the series want.