Pokemon is a great series I've enjoyed playing it for almost 20 years and this latest installment does have some major changes to it that not everyone is going to like.
Of course the most obvious change is that Pokemon GO takes place in the real world, your physical location (determined via GPS) is reflected in the game and important landmarks become PokeStops or Gyms. Pokemon can be found all over the world but after some testing it seems that Pokemon tend to appear more in public areas especially near PokeStops and Gyms, the more stops and gyms in a given area the more likely Pokemon are to appear. PokeStops will also generate 3-6 random items for users every 30 minutes this includes anything found in the shop except gold, and the loot table seems to heavily favor Pokeballs as around 85% of the drops I received where Pokeballs.
The most major change is the complete overhaul of the battle mechanics and capturing Pokemon. Turn-based attack selection is no longer present, instead users click on the target to attack and swipe their own Pokemon to dodge. This makes combat much more involved and action oriented than in previous versions. Capturing Pokemon is also much more different instead of first weakening the Pokemon the odds of capturing one are based off of its strength (CP), evolution, timing, accuracy of the thrown, and any tricks added to the toss.
In-app purchases have also made an appearance, however there don't appear to be any items for purchase that you can't earn in-game. There also aren't any "fast-level" items for sale however the Lure Modules can be a little OP especially when used in a dense area of PokeStops. On the whole however the in-app purchase items have NOT made it Pay to win, good news for all of my fellow cheapskates.
Pokemon in the world is a huge achievement the programming and effort that went into this is astounding. However the implementation does cause some problems on some mobile devices, extended use will drain your battery in very short order, it may cause your device to become uncomfortably hot (+40C on a Samsung Galaxy S4), I also had trouble where my GPS location would shift around 5-10m at a time which was slightly annoying. The AR is also an amazing feature it's really nice to see Pokemon wandering around the world, it would be nice if once caught we could view our Pokemon in AR mode.
The lack of new Pokemon, while nice for the First Gen-ers, does mean that the only "new" addition to the game is Pokeshops. Also the lack of interaction with Pokemon we have already caught is kind of a step back after the most recent 3DS games.
For the most part the release is stable and the only issues I had was caused by my device overheating slightly. There are some bugs present in the game (no not the Pokemon type) but none of them seem to be game/phone killers. Most of these bugs and heating issues are expected to be patched out "soon"TM. The menus are a bit laggy and the exit button can overlap with other things making it a bit of an annoyance at times.
Overall the changes are rather interesting and add a decent update to the series. However the game is currently lacking some key features that could make it absolutely amazing. Some features we'd like to see: A PokeCenter since currently only items can restore your Pokemon, more interaction with Pokemon (ex. allow us to view them wandering our homes with AR), classic battles as an option for 1v1 battles, trading, and public 1v1, 2v2, etc. battles.