Please forgive me, as I'm fairly new to the forums and my perception of the general vibe here isn't well founded. That being said, it seems the general sentiment around here is that Fallout 3 svcked, New Vegas was the best thing since sliced bread, and all of each has something to do with who developed what game. Having played both games (just finished my first play through of NV, actually) I just want to air my view, unpopular though it might be, and explain why I'm incredibly hyped for Fallout 4.
Let me start by saying I adored Fallout 3. Sure it was buggy, and sure, the main quest was a throwaway (par for the course when it comes to Bethesda), but I felt the tone and aesthetic they had was simply magnificent. While I have many cherished memories from that game, my favorite moment was quite simple: Seeing The Mall for the first time, specifically the Lincoln Memorial and the associated "free the slaves" quest. Knowing all that history, and seeing a post apocalyptic interpretation of it was, in my opinion, one of the coolest things to come out of gaming.
It seems from reading various posts on the forums that a number of people on here don't seem to like having all the US History elements, and would prefer a more 'modern, realistic experience'.
Personally I disagree; I love the bizarre interpretations and incorporations of pre-war history into the post apocalyptic world, and frankly that's where I found New Vegas to be most lacking (other than with Mr. House and the Legion, which were both great). I'm incredibly excited to see Fallout 4 be set in Boston, with its rich Revolutionary war history, and even more excited to see Beth capitalizing on it with the Minutemen, Laser Musket, etc. I suppose it's ultimately a matter of taste, but if brutal realism is your thing why don't you go play Metro, or S.T.L.K.E.R.- both do the post-apocalyptic thing quite well, while I think what makes Fallout unique is its fifties paranoia vibe.