Most of the people who are going "meh" are the people who loved the world Fallout 3 gave you to explore. This includes the locations, the total atmosphere, and so on. It's impossible to deny this game has improved on almost everything from Fallout 3, but those things aren't an issue here. What is at an issue is that Obsidian simply didn't make as good a world to explore as Bethesda did, and for some people, such as myself, those improvements just aren't enough to raise it past Fallout 3 in our eyes.
You know, I think you may have something here. Let me start by saying that I liked FO3...I was just disappointed with it because I really disliked the RPG mechanics, the core gameplay, the static and predictable storyline, the completely uninteresting characters, the fact that my actions as a player didn't matter much, and the fact that it really didn't come anywhere close to "feeling" like a Fallout game to me. That may sound like I didn't like it, but I really did...I just thought it could have been a LOT better than it was.
For me the core gameplay aspects are the most important part of the game and things like having a ton of locations to explore are secondary things that are nice, but not necessary. I'm a really busy guy and only get around 5-15 hours a week to play games, so I want all of my gaming time to be quality time. I'm not interested in squeezing many hundreds of hours out of a game. I just want the 40-150 or so hours I spend with a game to be satisfying.
Oblivion and Fallout 3 both have a ton of places to find and explore, and that's awesome. The problem I had with both of those games is that was the meat of them. While some of those places were interesting and had unique stories to discover, most of them were just samey mini-dungeons where I could find more Wonderglue, another glass dagger for my collection of >9,000 of them, a bit of money, scrap metal, some slippers, etc. Most didn't have any really distinguishing features. That would have been ok if I actually needed any of those things, but both of those games were set up in such a way that I didn't really need any of it. I felt like the exploration, while cool in small doses, was more of a time-sink than anything that was actually entertaining. I found myself wanting to know where the interesting stuff was so I could go check it out and move on. To make things worse, the sheer amount of stuff packed into the Capital Wasteland made it feel more like a theme park than a wasteland to me.
At the end of the day these games are a sandbox first and foremost and an RPG second...in some aspects a distant second. Nothing I did really mattered, from the way I chose to develop my character to my actions. In Oblivion I was head of the Mage's Guild, but nobody recognized it...nothing changed. In Fallout 3 I could try to create a character that matched the image in my mind, but by the time I was level 20 he/she was bound to end up being pretty much the same as every other character. At least a few skills were barely worth putting points into, but it didn't matter anyway because later in the game I'd find myself struggling to find ways to spend them. I found myself taking perks I didn't want simply because the game made me take one. With a few notable exceptions most NPCs were walking signposts at worst and robotic facsimiles of some character cliche at best. The atmosphere felt like a caricature of the Fallout series I knew and loved...garish and over-exaggerated. I was railroaded through a main storyline that, while having some high-points, was presented as though I were on the outside watching rather than an important participant.
Bottom line: the exploration is the meat of the game...there's very little to see when it comes to characters and there's very little interactivity for the player. You don't get to do things in the world that have any real effect on anything.
Ok, I'm rambling now.

My point is that I think you're right. For folks like me that are more focused on core game mechanics, characters, setting, and interactivity New Vegas is a breath of fresh air. For folks like you that are most interested in a sandbox where they can wander around and find tid bits and hidey holes all over the place I can see it being a disappointment. Don't get me wrong, I'd love to see more things to explore in New Vegas, but not at the expense of the other improvements they've made over Fallout 3. The changes made in NV largely address my biggest disappointments in Fallout 3. Maybe Fallout 4 will be a good compromise for both types of players. Here's hoping. :foodndrink:
Edit:
Holy crap, wall of text. Didn't realize I typed that much.
TL:DR Edit (just for you, Mr. Fish):I think I agree with you. Fallout 3 left me cold because it was first and foremost a sandbox and I felt its core gameplay, interactivity, setting, and story were lacking. New Vegas addresses these issues, but doesn't have as many places to find as Fallout 3. This is fine with me, as the core gameplay and interactivity are what I'm after, but I understand how the scroungers and dungeon hunters would be disappointed. I'd like to see more of that too, but not at the expense of making the rest of the game feel as hollow as FO3 felt to me.