A fairly inexpensive game, worth hundreds of hours of whatever you choose to make out of it.
There are literally no downsides to purchasing this game, even without any of the DLCs.
The DLCs were added later to add more content to a game that had gotten dry for old players.
So if you haven't played it yet, I highly recommend it.

(Edit: This game is a timeless classic. Even getting past the outdated graphics, which you could install mods to fix; this game has better world building than any other Fallout game besides maybe 1 or 2. Fallout 3 got very dry for me after my first couple times playing it, because there wasn't that much to do outside of the main story. Fallout 4 suffered from the same issues before the DLC launches. I'm certain Fallout New Vegas will remain as one of my favorite games for the simple fact that even just walking around in it is fun.)