Basically they're running out of ideas.
I mean, it was bound to happen and well, it has. I would like to think that this will be the last generation as it has been dragged on for a bit now. As much as I would hate to see pokemon go, I'd prefer it to end on a good game/generation then end with no one playing it anymore due to how rubbish the pokemon designs are or how bad the games are.
I've preordered the steelbook version of Sun, mainly for the figure but also because I love the steelbook. Thinking back, I hardly thought about the game itself but whatever. Pokemon sun looks the better of the two, mainly because I really like the look of the legendary.
Some people will disagree with me that they're loosing ideas, but after 7 gens it's incredibly hard to keep pumping out ideas. One person said to me that if there's money there's always ideas. That's true to a certain extent. If they're money, and they want money incredibly badly then yes, there will be a somewhat constant stream of ideas which will slowly get worse in quality, that route will end in people not wanting to buy the product due to low standards of the design. The other route is when they don't care much about money and are fine with ending the series by themselves. That route means that you know your limits as a desiginer and you can see the quality of your ideas getting worse. So you make one final game/product, make it the best you can and end it on there. From there you can make spin-off with the same characters, remakes, whatever without needing new ideas.