HMs have been the scourge of this series for a while, which is most apparent in this gen even in the definitive edition. While platinum makes so many improvements and additions I couldn't possibly list them all, the game is still a bit slow overall. Other than that though this offers things other later entries have continually failed at.
The difficulty curve is excellent, because of this, my hardcore nuzlocke is one of the most challenging and memorable moments I have had with any game. I grew so attached to a ponyta that I was close to tears when it was killed a riolu's counter. But then I got a riolu for myself and took him from level 1 all the way to the league and that fucker absolutely redeemed himself by not only 1shotting cynthias garchomp with a critical close combat, but also DOING IT THE NEXT TURN TO ROSELIA WHO RESISTS IT.
Battle frontier will likely never comeback, for which I am very resentful. I've spent far too much time in the battle factory alone.
Finally the story has some dumb moments (the literal terrorist attack in Pastoria) but it has tons of potential. Cyrus is a legitimately excellent manipulator with a deeply hidden backstory. The distortion world is the pinnacle of this game and summarises the entire experience for me: It may be slow but it is a challenging and immensely memorable journey.

It boldly tries things no other entry had ever or will ever replicate because they were vilified on release. I will never understand why and as a result, the series went into decline. Everybody loves it now, but unfortunately, it is too late. Enjoy your easy and soulless romps critics, its what you asked for.
My only criticism is that Patrat exists.

This review contains spoilers

I'll start with the positives, all 2 of them.
I don't usually praise the soundtracks of these games simply because it's just given that they are exceptional. This is thankfully very much still the case and there are some very memorable town themes.
I like megas, I don't like the gimmicks they inspired, but this one works, if only in a competitive sense. This brings me to my major praise: this is perhaps the best metagame in the series. There was an oversight that did not increase the speed stat on the first turn of mega evolving, but I actually think this added a layer of strategy to an overwise overpowered mechanic. Sure seeing Lando T in every game sucks but that was the case last gen and for as much as I love gen 5, that games meta is just weather wars.
Ok other than that fuck this game. It's insultingly easy. The characters are lifeless and the story falls flat on its face as a result. The villain (I don't even remember his name just his stupid hair) wants to destroy the world which could've made sense in a pure evil cyrus/ghetsis way, however, there's a moment at the end where he admits Pokémon have to die too. It tries to make him seem resentful and pull at your heartstrings but it just makes him seem like a fucking buffoon. Did you not think of this? Why carry out all this if you don't even like what it results in? I guess the history and the timeline diversion stuff is semi-interesting for the series as a whole, but it culminates far better in the delta episode of ORAS than it does in this entire game.
Good meta, abysmal generation of Pokémon.