Seems like I share the opinion many of you have: I'm relatively unimpressed. A bit sad, really, considering we're on a Pokémon board. I understand they don't want to reveal too much too soon, but I've come to loathe how TPCi's MO is to show off as little as possible upon reveal -- and proceed to reveal 90% of the new features before release, anyway. Show off more in the beginning so you can better spread out the information and build hype gradually.
Another part of my disappointment stems from the fact that USUM appears to be taking cues from what I believe to be the worst part of the "extra" games: like the third versions, the story sounds to be relatively unchanged, and like the sequel games, there's two of them, each focusing on an apparent fusion. I hope there's some amount of "sequel" to USUM, otherwise I'd prefer if they had just made a single Stars/Prism/Eclipse.
That being said, I'm sure my opinion will change as we see what USUM is really all about. Maybe there will be some bigger changes to the story than it currently seems; gyms in those empty plots would be a good start.