To start, assuming the creators built New Vegas on a previous built engine and models, it would seem that the world would be bigger, more elaborate, and with an environment that you can almost fully interact. However, half the buildings in the towns are boarded up and invisible walls (not the terrain) keep you from entering parts of the world that are unobtainable. I do not want to speculate why certain areas are unobtainable, but considering the tools made available by Fallout 3 I would expect an improvement not just in this area but overall. New Vegas feels more like playing the previous version that Fallout 3 was built on, instead of vice versa.
I myself don't like invisible barriers either but I understand why they are there. The bottom line is this, if you get around them, you break the game. Case in point..the cliffs north (and general area around) Black Mountain. There are clearly areas you should be be able to climb up but aren't able to. If you were, you could technically snipe down the super mutant area without anyway for the AI to path to you - breaking that area. My impression of invisible barriers is that, over the time of testing, spots where the game could become broken are found, and in the interest of time, invisible barriers are put in to correct for these unintentional situations. FO3 had these also and were annoying...case in point - the metropolitan area around the Capital...you would see the wreckage of a building wall which appeared to be scalable and you would simply hit an invisible barrier at the top. I'm sure those were placed for the same reasons. So to say that this is a new development in the short comings of world building wouldn't exactly be accurate.
I could continue on, on other various components of the game, but I came to this website to see what was being done regarding all the complaints I’ve heard and read about, only to see on the first page a bunch of reviews averaging New Vegas has a 90% gaming score. I’m not being tonal and I want Bethesda to be one of the brands I look at in games with high standards that produce quality goods and stand by their name.
90% is an outstanding score...considering much of the same components are directly being borrrowed from an older game...much less any game.
I would really like to hold Bethesda in high regards in the gaming community and would hate to see no more midnight releases of their titles due to corporate economic reasoning. The bottom line is important, but as many have forgot so is how you get there. Figuratively, do you really want to hold out a C paper and say we put our best foot forward?
Well it's too bad it didn't fulfill your expectations but for many, like myself, it did.