The Google Play Store is the default app store for every Android device using Google services.
Con Must have a Google account
Apps cannot be downloaded from the Google Play store without a Google account. While that's not a big hassle, and it's useful in keeping your account synchronized, it would be nice to have the store act as an app server, for those who don't wish to open up a Google account.
Con Zero quality control
There is absolutely no quality control on the Play Store whatsoever. AAA publishers constantly get away with purchasing five star reviews from click farm businesses while at the same time game spammers get away with flagging legit games that they have stolen code from and published as a clone.