Heh, thread seems to have died down with all the hype for Fallout 4, that people have started talking about Fallout 3 and Vegas over there
Anyway.
I finally installed that Tale of Two Wastelands mod, and moved my almost-level-50 character over there (and now every scorpion is an Albino Bullet Sponge), and it's interesting to be able to compare them side to side in the same play session.
Not even going to talk quests or story or gameplay or stupid kiddie cave towns.
One thing I like more about Fallout 3 is how the DC wasteland looks. It definitely feels bigger, not just area wise but all those tall buildings that you can't enter, I missed that feeling of a city. However, the thing is really empty. When playing NV, when standing at any landmark, even with crap Perception (not sure if it helps or not) you can always see one or more unexplored landmarks that you can walk towards. In 3, if you don't have a Quest Mark, you have to pick an empty direction to walks towards, and hope that eventually a hollow triangle appears so that there's someplace to go. This can be considered good and bad tho, for those who think that magic compass markers are immersion breaking.
About impassable terrain: this irks me in both games, but in Fallout 3 is more blatant railroading. In New Vegas, they took a few "hilltops" and decided arbitrarily "thou shall not pass... unless you walk around it and thru the opening". But almost none of these areas are important for quests, most of the times they're like valleys or canyons where you can find a skillbook or some crap. And they did this because they meant for the terrain itself to be "too steep" but people would always find the small ledges to slowly inch upwards. I think it's stupid and pointless and no game has been ruined forever by the mods that remove these invisible walls. But at least the walls are hard-ish to reach.
The only part of the game where I felt this had a point was the Boomer base (so you had to go thru the artillery gauntlet). I never even tried climbing around it, for some reason... but if that's the case, it would be trivial to make some sort of makeshift wall around their area, like the Strip has, atop the mountain or something. Or even some crappy indestructible plywood fence.
Fallout 3 however... these are blatant checkpoints. They are meant to force you to go to the annoying subways. Mandatory spelunking, bleh. Many of these are even empty but you waste your time sneaking anyway just in case. And the impassable "rubble piles" are tiny mounds that can be climbed with little to no effort, then on the top you find out there's an invisible wall. And the only reason this stops being annoying is because you can fast travel and bypass them once you explored for the first time.
In short, I like the terrain of DC Wasteland better (city included), but Mojave feels more alive in many ways (way more pristine too, with proper yet sparse vegetation). Invisible walls are either stupid and pointless (NV), or stupid and blatantly railroading (3).
Also I hate the DR bullet sponge system of F3. It makes so that what gun you're using is irrelevant vs. how many DPS you can put out there. Damage Threshold does make you at least have to consider using large calibers for some targets, even tho you can still plink enemies to death of a thousand 10mm rounds (it has been argued that the original system of F1/2 was better, where DT was usually lower but could lower damage to 0 vs the NV system where 20% of damage goes thru regardless).