To be fair, FNV's map apart from NCR and Legion hit squads didn't have any random encounters. The world in terms of what NPC's roams it feels very static. Walk down a road and you've pretty much seen everything that road has to offer for any subsequent playthroughs. FNV's map is also quite desolate of 'stuff'. Which makes sense, since it is a desert, but even so I can understand that criticism. FNV's strengths lies in its quests, characters, RPG mechanics and writing. Everything else is either 'meh' or flat out bad. (and a lot of it was inherited from Fallout 3 (which would make those critics hypocrites if they don't condemn Fallout 3 for the same things))
FNV's vanilla map is boring because its supposed to be boring. It's a fucking desert after all. So they're right. But at the same time they're wrong. Because like I said, it's a desert, what were they expecting out of it?