The biggest issue is it doesn't really have any mechanics beyond "catch pokemon". There's not really gameplay, short of the laughable gym battles. You can realize this after about a half hour of playing. Nintendo is sitting on top of a big giant pile of money, but I get the feeling they want to gimp Go in favor of their mainstream games.
Seriously, all they need to do is add a basic pokemon PVP with the same battle mechanics from the mainstream, and maybe random events, and they could keep it going for a good while longer.
Also, the always-on-gps is a huge issue with it. They need to find some way to lessen it.