All in all, I liked SuMo, and I have to say it's worth getting, even if it took me a long time to get around to finishing the main story.
Team Skull is definitely lighthearted and silly. It actually makes it interesting to see some of their dialogue. They also did a pretty good job of really giving Kahunas and captains their own personalities. They're far more active in you quests than they've ever been in previous games. The people themselves are all a lot more varied in type in a way that makes this game feel really down to earth. There are even several times when you know the game is being self-aware and poking fun at some of the things in the games themselves.
The game just really drops the ball on the player character's expressions. With everything going on and everybody else showing a wide range of feelings, the main character stands there like a rock with the same empty look he/she has on the entire game. It would have been nice to have a simple choice between reaction emoji's, like they kinda sort of did in Golden Sun.
I also really liked the huge variety and selection of pokemon you can capture and raise right from the start. Where the Reborn game is begrudgingly giving you a new mon at a time like it's pulling out its own teeth to do so, SuMo gives you so much if you take the time to explore.
Island challenges are nice and succinct. They aren't difficult to do nor do they ever feel like they're making things drag on or are a chore. The islands themselves are small but they're all in tidy little sections that do a lot with a little bit of space. In my opinion, this really helps keep the pacing great and you aren't buying boatloads of repels to get through them. Of course, HM's are out and the ride system is a great replacement for them. They've thankfully cut down on the really annoying things of the past, like having to manually select a pokemon to use the move to deal with a barrier, or having to sit through a drawn out animation of a silhouette doing the thing (remember cut and fly and rock smash, and constantly getting asked if you wanted to do the thing you clearly want to do?). It happens more quickly and realistically so that it doesn't make exploring a drag like it used to.
Remember nugget bridge, where you had to face all the trainers on the bridge, then fought one last guy who gave you a nugget for winning? They did something like that with most of the major routes. There's one person who won't fight you until you beat everyone else in the route. Once you return to beat him or her, they usually have some move, item, or technique to introduce to you during the battle (and they usually provide you with a pretty decent challenge). When you win, you could get an item like a Red Card, or flame orb, or even a TM, usually based on the strategy they were working with. This is a fun little system that I think works very well to educate new players on some meta strats and rewarding players whose completionism makes them take on all the trainer they find anyways.
Pelago is actually a really nifty new feature that really helps out, especially players who might have long stretches of time in between play sessions. It can get eggs ready to hatch for you even when you aren't playing. It'll EV train a stat for pokemon while you're maybe grinding out levels or ev training pokemon in your party. Or even level 'em up for you, since the daycare doesn't raise levels anymore and is purely for breeding (cuz hey, that's much better when your daycare mons can't level up and accidentally overwrite that egg move you wanted to breed on, etc). You can make those boxed pokemon find evolution or selling items for you. All your berry planting is in one place and you know when the berries will be ready to pick. It's really a major convenience that I'm glad they added in the game.