[XltSystem]

Yeah there were meant to be 151, but 6 aren't released, due to all the botters and snipers(spoofing location to the exact location of a rare spawn).
Once you catch all of the ones available you get this :

Spoiler:

Nothing. You can brag about it to people but i don't really enjoy doing that.

So basically, once you catch them all, the game comes to an end without any further challenges?

If that's the case, I think the developers should've put a little more thought Into It.

You can still walk around and catch Pokemon etc, but yeah it was slightly disappointing. There is PvP involved, but that too is very disappointing as its not technically PvP (You are fighting a real life players pokemon, but it will be controlled by an AI that is easy to predict)
I agree, they should have put some more features, especially for players quite late into the game.