I'm a huge fan of Balor. Out of everyone in NXT, I think he has the best chance to become a star in the WWE once he's brought up. He's extremely marketable. His Demon persona and entrance is unique. He's a great performer. While he isn't a great or even good talker, it's easy to work around that, especially considering his Demon gimmick.
Unfortunately, therein lies the issue. That is what Balor is all about at this point, which wouldn't be a bad thing except that is a once in a couple of months kind of thing. Even if he were on the main roster, we're still only talking once a month. I have no problem with that because I don't want the special feeling you get when he enters the arena with his body paint to become nonexistent due to it happening every week. However, Balor's character needs to grow beyond that. We don't have much of a reason to invest in him beyond that. If you're not going to do that, then at least put him in a meaningful storyline. For the second time, Balor is the #1 contender for the NXT Championship and yet, he has taken a backseat to everyone and everything. He hasn't had a rivalry yet (hell, Riley spent more time feuding with Owens than Balor did) since the whole Ascension saga. The only thing he seems to do is win at PPVs and then make a couple of NXT appearances now and again. They haven't done anything meaningful with him.
A lot of that has to do with the 1 hour time constraint. They don't have a lot of time to develop much of a story outside of the titles. They could still do a lot better than they are doing though.