For the main games, Sun and Moon are my least favorites. (I haven't played much of USUM, though, so I can't comment too well about how they compare to Sun/Moon.) While they start off with some of the main elements seen in Pokemon games, they spend too much time breaking up the flow of gameplay with constant cutscenes and unskippable tutorials. That wouldn't be so bad if they let up fairly early on, but the same pattern persists across several islands. If anything, it feels more like I'm going on a supervised field trip through Alola with Has and Lillie, with a little bit of time to explore on my own. As a long-term player, I've found the experience fairly boring, and there isn't a decent post-game to offset the dullness of the main game.
In addition to the constant tutorials and interruptions (seriously, couldn't there be a menu option where we can indicate that we've been playing these games since long before our companion characters were born?), the story didn't appeal to me very much. Part of the problem is that Lillie is central to the story (as opposed to the player character being the story's focus). As someone who didn't like Lillie, and frankly found her annoying, it seemed like I had to keep interrupting my own journey to listen to Lillie's plights and occasionally get her out of trouble.
That said, Sun and Moon aren't bad games. They just didn't feel as much like Pokemon games as I would have liked, between story changes, lack of gyms, and various other elements. I may be unusual, but I actually like stories where my character is central to what is going on, and if anything, I would rather focus less on the plot and more on my character's development as a trainer. And while I understand that GF designs these games for children, I made it through gen I just fine with far fewer tutorials and linear roadblocks, and I suspect modern kids could do so as well. Perhaps GF has come to underestimate its audience's abilities.
We'll see what happens with Sword and Shield. I liked the trailer, though there's no indication that those games won't share certain irritating elements with Sun and Moon. But at least it seems like S/S will be traditional entries in that they'll have random encounters, wild Pokemon battles, and gyms. Personally, although I would love to see the games return to the level of content they had in gens 4 and 5 (with battle frontiers, etc.), I would be satisfied if gen 8 resembled gen 6 (traditional format, fairly safe design choices, some nostalgic elements thrown in). I've been feeling fairly apathetic about Pokemon of late, and I'm hoping that gen 8 will help change that for me. I tend to get more invested in even generations than odd ones, and I would say that even generations tend to be safer in their design choices (they don't tend to have complete reboots in terms of Pokemon available in the main game, for example), and I'm hoping that gen 8 will continue that trend.
