Wall of text incoming. Also spoilers.
The highlight of the sequel trilogy has always been the chemistry between and amongst the leads. RoS has that in spades-- makes it, in fact, the fulcrum upon which the movie rests. The connection between Rey and Kylo, and all that this enables and entails, is as solid a foundation as you could hope for. The actors sell it so well, even with the movie doesn't know what to do with it. Finn punches above his weight, as well, bubbling with faith-- in the Force, in the cause, in Rey. The other characters are as well drawn, charming and engaging and slimy as they should be, depending on who we're talking about. They carry the movie.
It's a movie that badly needs carrying because of flaws both subtle and gross, both generically applicable and unique to the Star Wars mythos. It's too easy to call it a bad movie and leave it at that. Make no mistake; it is. But it is one that is able to push enough buttons, to lean on its stars and wars just enough, to be a worthwhile diversion.
We can start at the micro level. One of the rules of fantasy or sci-fi stories is that you can make whatever rules you want, so long as they're consistent. Barely a few minutes in, RoS violates this with its "hyperspace skipping". The first time we hear about travel through hyperspace, it's from Han "never tell me the odds" Solo, who insists that they jump only with proper calculations done first. In RoS, the Falcon makes multiple jumps in rapid succession with nary a mention of doing the math first. I was annoyed when Cassian did a single jump in Rogue 1; this movie amplifies, magnifies the mistake. Almost as bizarre: the TIE Fighters following the Falcon follow it in its jaunt. Tracking through hyperspace was introduced in Last Jedi, of course, but it was resident only on capital ships.
There is, throughout this movie, a tension to it in its relations to The Last Jedi. Some things it explicitly undoes, such as Rey's parentage or repairing Kylo's helmet (only for Kylo to doff it for good in the first 1/3rd of the movie); other things it grapples with uncomfortably, like hyperspace tracking, and some it handles clumsily, such as Finn's hurling at Poe "You're not Leia" (when Poe's main character arc in TLJ was growing into a leadership role Leia and Holdo were grooming him for).
Because of this entanglement, some people are using RoS as an opportunity to relitigate TLJ-- either accusing RoS of trying to bury the better movie, or blaming RoS' failures on TLJ as the unworthy predecessor. I would say that RoS commits plenty of unforced errors; many of its decisions, like hyperspace skipping, are bad in-and-of themselves, regardless of where the ideas originated.
The weirdness starts almost immediately. Kylo confronts zombie Palp and puts his lightsaber to Palp's throat. Palp offers him a fleet if he'll kill Rey. Kylo agrees, only to leave so he can go recruit Rey so she'll come with him to kill Palp and... seize the fleet...
That is, the plot only happens because Kylo inexplicably decides to take the long way around to something he could have done in the first two minutes.
This is typical of the movie: choices are made for spectacle or to give characters things to do, rather than because they make sense. The cavalry charge across the deck of a Star Destroyer turns out to be as inexplicable in the movie as it was in the trailers. Per the story, the Star Destroyers' shields are down because of the environment; in that case, if the goal is to destroy the Star Destroyer's comms, wouldn't a single starfighter strafing run be far more effective than a boarding action? If the bad guy who stabbed Rey's parents needed a wayfinder, knew he needed one, and knew where it was, why didn't he just take it instead of engraving its location on a dagger so he could come back later?
The movie makes an ambitious grab for Lord of the Rings' record-setting number of death cheats. Rey is afraid she killed Chewbacca when she blew up his transport-- oh, but he was in the *other* transport! C-3PO's memory gets wiped-- ha ha, jk, R2-D2 has him backed up. Poe's spice runner gal pal (because if we're gonna make Poe be like Han he's gotta be LIKE HAN) gets blown up along with her planet... oh, turns out she has a ship after all, good timing. Pulling this sort of thing repeatedly makes us feel as if there are no stakes. This is a series in which character deaths have meaning. When plot armor gets too visible it undermines the whole enterprise.
The film also has some JJ Abrams-specific quirks and failings: an abundance of bottomless pits and nary a guardrail to be seen; superweapon inflation; a complete mangling of time and space scaling. The Star Wars galaxy has never been large, but Lando traversing its breadth, rallying a huge fleet and escorting them all to the site of the battle, in a matter of... what, thirty minutes? Maybe an hour? I know the Falcon is fast, but darn!
And yet... when that rallied fleet arrived, when they came to the rescue when all hope seemed lost, it was still emotionally affecting. I reacted to it.
The movie can do that. It has that power. When Rey slipped Ben the lightsaber through their ForceTime connection and they engaged their respective foes in parallel, it was awesome! And when Rey and Ben came together to engage Palpatine...
...the movie let opportunity slip through its fingers.
Duality is a theme of these movies, of the Force writ large. Some people were weirded out by Rey and Ben being a "dyad in the Force"; I dug it. It was foreshadowed in TLJ and paid off brilliantly here.
For one to live and one to die, even in the fashion in which it's done here, is to let the promise of that concept go unrealized. It's especially so in light of the Kylo-Rey relationship. What Kylo offered Rey-- explicitly in TLJ but implicitly here-- is the promise of belonging. What Rey offered Ben was acceptance and forgiveness. Those are powerful themes! There are so many things they could have done, directions they could have gone, in mining those themes. Instead they flee from them.
There's so much more I could talk about, so many choices that are weird or ill-fitting or that don't pay off. But that, I think, is what I come away with most strongly from this movie: that sense of squandered potential. RoS is an entertaining but bad movie. It could have been so much more.