I've not completed the main game yet, but after 90 hours of gameplay and 3 out of 4 dlcs, I've reached a fairly precise idea about this game, with its plus and minuses.
About the main game.
As many have already noticed, the game is initially flat, and the locations are quite boring. There's not much variety, even if I've found some interesting places such as Hoover dam (NCR Base). The overall atmosphere of the game is pretty weak, with very little variety and poor design. I'm quite dependent on atmosphere and graphic compartment, and NV from this point of view is a pure failure. Fallout 3 with the same engine has far more charme than NV.
The idea about gaining or losing reputation with groups and factions is really good, but it is not immediate and intuitive and it is very easy to mess with the various groups. What initially struck me down was the fact that after killing some ambushers (that had attacked me without reason) near Goodsprings, I still remember well I had lost reputation with that place inhabitants, risking to screw up already one of the first quests. Quite annoying! After getting used on how it works, it becomes easier to do "the right thing" for "the right group", but still, it remains quite easy doing the wrong choice during a quest that screws up the mission tranforming the pc in the enemy of the group he was trying to join (Brotherhood of steel, crappy people!).
The weaponry is extremely various and rewarding, I really loved trying such variety of firearms and energy weapons, even if I was almost always low on ammunition; this brings a good idea of "survival game" in which New vegas is really good, even if sometimes it is frutrating; the armor compartment is quite poor instead, I've survived beyond lvl 30 always using medium-light armor, and just actually I've managed to obtain some decent gear (the riot gear in lonesome road). Most gear is quite crappy, and I haven't seen the classic power armor, except the type used by the Brotherhood of Steel, that now are my enemies.
Old world blues. Well, I've found it quite boring, with low survivability. It has been quite hard for me to go through the story, that didn't capture my interest, and the overall gear obtained at the end of it is not worth the boredom I felt.
Dead money. The idea behind this DLC is quite good, and there is much charm and atmosphere in the maps I have explored, but to be honest it is the most irritating game I've ever played, with a lot of runs to reach the next safe place before having my head exploding and the crappiest gear and weapons I've ever used. The level and traps desinger must be a little sadistic!The enemies are well designed, but not very various. I'm not going, anyway, to spoil what kind of monsters are present.
Now I'm playing lonesome road and it is actually the best part of the game I've played. It has, till now, very atmospheric environment (even if very linear) and very good gear and weapons as a reward and as tools to play through it. Finally I got my cool Riot gear, even more beautiful than the NCR ranger one. This dlc reminds me somehow one of the Borderland 1 dlcs: the Secret armory of general Knox, and for me it is a very positive thing. I'm actually enjoying a lot this trip along the road!
Ok. This short list of impressions is my overall idea about NV. It is far better than I previously thought, but still it has many weak points.