Finished the main story. I'll keep this fairly spoiler-free. Overall, the game is charming yet fairly inoffensive. Gameplay wise it sorta just hands you a huge amount of tools to shatter the difficulty with if you want to, and even encourages it in some ways. However, there is one particular boss towards the endish of the game that will likely catch you off guard. It's nothing ridiculous, but it's notably harder than anything else in the game and there's a pokemon you're given as a prize right after without any opportunity to save between claiming it and the boss (meaning you have to fight the boss each soft reset attempt), but this is only really an issue if you want that particular mon for competitive play. Most of the clunkiness of SuMo is gone, but you're still railroaded pretty heavily, although not to the degree of Gen 6. The alternate story is quite nice, and while I think they could have expanded on a couple of the things they teased before release, the changes in character development are a lot more interesting than I initially anticipated. They didn't completely save my opinion of some of the characters, but I appreciate they made the effort to try. If you absolutely hated Sun / Moon, you probably won't like this. If you were neutral on it or enjoyed it, you'll probably like this a lot.
I'll write another post when I finish the postgame, but it looks incredibly promising.
If you're a competitive player, the changes in this game are looking very promising for both Smogon and Nintendo Official formats, so I'm really looking forward to teambuilding and playing online.