Those people that have spent 100+ hours on the game probably don't work or have many responsibilities (I have a considerable amount of time spent but I'm also in college). I sympathize with you though. I don't see why someone who dislikes a game so much would spend so many countless hours playing it (if I hate a game I usually know in about an hour) let alone spend the entire time comparing to another game. If I had such strong feelings against a particular game, I wouldn't play it. I'd play a game I like more. In this case, those people who rue purchasing Fallout: New Vegas would probably be better off selling the game and going back to Fallout 3.
Who knows? Maybe some people just have the irresistable urge to complain.
Edit: I see many people complaining about invisible walls and blocked paths by means of strong enemies.
It's true that you run into some invisible barriers, which is a little disheartening to say the least, but all Bethesda did in Fallout 3 was disguise them better. I was surprised that I couldn't climb over a pile of rubble in the urban areas of Fallout 3 (I know it's possible considering that I've done things of that nature before) and see what's on the other side. Being guided down into the sewers to get around was annoying as hell. The majority of those invisible barriers I've found however just kept me from going where there isn't anything anyway and the others I had to go pretty far out of my way (I've found three, maybe four barriers total in my entire 70 hour playthough).
As for my path being blocked, I was somewhat relieved by that. I made the mistake of skipping ahead in my first run through Fallout 3 by going to Rivet City... I missed out on a major plot development, never met Three-Dog (which is good, because I probably would've shot him.), and never fixed the radio antenna. I lost out on hundreds of xp points and discovering the Capital's Mall. As for Fallout: New Vegas blocking your path North out of Goodsprings, that's the only time I can think of that the player is ushered in a certain direction by means of enemies blocking the way and the only reason I figure Obsidian designed it that way was to help ease the player into the game instead of letting the player rush off to New Vegas. The entire drive behind the first section of the game is the player character's drive to find the man that stole the platinum chip but you don't know where he went exactly until you make it to Boulder City. Sure, you could skip ahead and forget the entire first section of the main quest-line and lose thousands of xp from it and the other side quests, but why would you want to? So you could try to sneak into New Vegas?
That just doesn't make sense to me.
