^This
As well as, all in all, there are many more places to go ,besides the countless metro tunnels in 3, in NV. Deathclaws are scary as hell! Boom boom boom dead, and I'm a level 20?! F that man, Imma go find a fat man.
New vegas is more challenging, more fun, and hardcoe mode is a huge improvement.
IMO there's actually less areas with truly challenging enemies in New Vegas.
Since there is no random encounter or level scaling system, you have a few Cazadore and Deathclaw-filled areas that are extremely hazardous for anything besides a near-max character. However, aside from those, a lot of the locations are bunched together, and they really aren't that tough.
If you were a high level in FO3, there were always high-level opponents facing you. This was most notably with Broken Steel, which added the incredibly tough Overlords, Albino Radscorpions and Feral Ghoul Reavers, but it happened in the vanilla game as well.