Sunlight is evil, therefore I can't play it 
I also have better things to do with my life such as playing other games that don't involve going outside 
The idea is interesting though. I played a game with a similar concept (geo location based games) called Ingress. I find that these games encourage people to waste fuel and to pay more on their phone bills. Though they do encourage socializing and exercise (if you don't drive everywhere).
With Pokemon Go, you cannot walk/move faster than 5 km per hour or it will not count towards the distance accumulating towards hatching your poke-eggs. ( I know because I was running to try to hatch faster and it counted NONE of the 5 km I ran :c)
I'm sure it's a nice game and all. And I'm glad it's getting people outdoors and socialising more. But there's a downside as well from what I've been hearing and reading. Too many places are banning people from playing the game, people are getting injured or looking for Pokemon in the wrong places, and so much more.
While many people are kind of stupid and are looking in the wring places etc, the game at the very beginning warns you to remain alert of your surroundings. The phone will make a noise and/or vibrate when a Pokemon is near. There is also going to be an addition to the game in the near future where people can pay for their location (if not a historical/ interesting location) to be a Pokestop. Also, in the near future, I hear that they are also adding a request for removal of a Pokestop.
People are also complaining about the servers crashing all the time but Niantic is a tiny company that has recently launched arguably the most popular (mobile phone) game in years in several countries all around the world.
