It's not like temporary invisible walls bad or "omg we'll clear this rockslide once we get the [mystical dynamite]" bad, but they do attempt to lock you into one direction at the beginning of the game. Some mountains near the edges of the map look climbable but do have invisible walls, that's a separate issue that FO3 had too.

In NV, you start in Goodsprings, halfway up the map and most of the the way West. They tell you to loop around by going South, East, and then back North to get to New Vegas. They enforce this by surrounding the area North of Goodsprings with huge masses of three of the deadliest enemy types in the game (Deathclaws on the Northern road, poisonous Cazadores to the NW of Goodsprings, and Giant Radscorpions due East of Goodsprings). One of the NPCs actually says that you'd have to be the biggest badass ever to get through the Deathclaws.

So it's not impossible to go straight North to New Vegas, but they make it really, really, hard on you at the single digit levels.

The high level critters scattered in all the shortcuts make it tough to explore at low levels. There is a slight charm to that too, making the Mojave feel quite deadly to the unprepared, but it's kind of a drag.