I like how it's a game that encourages you to get out and go on walks. Wii Fit is the only other video game I can think of which incentivized actual exercise, and didn't really do that very well.
I don't like how the media makes it out to be some "safety risk," because of dumb people oblivious of their surroundings getting into accidents and walking into walls. Play it responsibly and you won't get injured.
I don't like how draining it is on my phone's battery, though I can't say I'm really surprised, given that you have to keep your screen on and have your GPS on while playing it.
I don't like how the social aspects of the game are really, really limited. For something Pokemon themed, the social part of the game should've been a much huger component than it is currently. Even the gen 1 games had more meaningful social interaction, and those were what, 20 years ago?
All things considered, I like it. It has a lot of potential and I have hopes for it, but I can also see it going the way of Candy Crush. You know, one of those pay2win games with no meaningful gameplay? That seems to be the trend that
every other mobile game has followed, and I fear that Pokemon Go will go the same route. But until/if that time comes, it's entirely probably I'll log more hours on that game than I will on DDO.