I loved Gen 4 and Platinum, so I'm enjoying it so far. It's *very* close to the original DP story, though, so if you didn't like it then, you probably won't like it now. All of the main story beats from getting your Pokemon onward have been from the DP story so far, no sign of Charon or Looker, available Pokemon and encounter charts are based on DP rather than Pt, and so forth. Otherwise, it's a huge nostalgia-fest in both the big ways and even in little touches (the battle cut-ins and starts are basically straight from the originals before shifting to a panning camera like modern games, f'rex). Also, the town map tells me Battle Park instead of Battle Frontier is in the not-Kurils, which is unfortunate but after ORAS, unsurprising.
Gameplay, I'm not convinced about the Contest changes (one-button rhythm game instead of the original type with moves), and the tile-based layouts sometimes are a touch finicky with the analog stick's free movement (D-pad movement does lock to the tiles just like older games). Otherwise, HMs are gone entirely: everything's now TMs, which are breakable again, and while you can use former-HM moves just as you could in the original, the Poketch also has a new app that lets you call in free HM help from wild Pokemon once you find the TM and get the badge. Live PC access in the field is surprisingly convenient when leveling, but speaking of leveling, it's far too easy to get horribly over-leveled even with what I suspect are EXP rubber-banding features. An EXP Plus-alike (half-EXP to all Pokemon in the party) seems to be always on and I haven't been able to find a way to turn it off in the game options or item screen yet. Combined with my penchant for catching everything in the Grand Underground where wild Pokemon level based on badges in multiples of 10, I ended up rolling over the third and fourth gyms with Torterra.
EDIT:
I'd kinda like to know how the remakes handle Dexit, speaking strictly as a non-Switch-owning outsider.
Looking it up, Sinnoh's national dex is the same as in the original: all 493 Pokemon from Generations 1-4 should be in (either available, tradable, or coded in for future events), and as far as I can tell without spoiling myself, nothing else (absent patches).
EDIT 2:
Having beaten the Elite Four and Champion and entered the post-game, some additional thoughts:
1.
Heavens, I forgot just how rough the Sinnoh Elite Four and especially Cynthia could be. That even includes Flint's fire-hot DP team with a whole 2 Fire type Pokemon (and Lopunny). Flint's Minimize/Baton Pass tactics are still just as entertaining as they were in Gen 4, and it's kind of embarrassing how effective of a wallbreaker Lucian's Medicham was against my team. And then there's Cynthia...I was still terribly overleveled due to how the game handed out EXP like not-especially-rare candy, but it was a closer shave than I would have expected due to lack of proper EV/nature training. Amusingly, it was her Flame Orb/Marvel Scale Milotic that gave me fits rather than her Garchomp, because my Electric coverage was on solely the physical side.
Also, the Elite Four and Cynthia get their Platinum teams on subsequent rematches, so that's also a thing.
2. Can confirm that Battle Park is not an inaccuracy on the town map: they did use the DP Battle Park instead of the full Platinum Battle Frontier. They do have all sorts of things to make training Pokemon easier, though: Bottle Caps to maximize IVs, Ability Capsules and Ability Patches to switch Pokemon abilities to their standard or hidden abilities, and Mints to change Pokemon natures. I do so still wish we had the Battle Frontier to let us use all of these lovely tools in more places, though. Heavens, I would even *pay* for it (eventually); I did once already with Platinum, after all, and DLC at least is cheaper than the full remakes were.
3. Full gym rematches also returned even if the Platinum Battleground did not. Roark drops by to call you out on behalf of everyone when you get the national dex.
Ultimately, I suppose my opinion is unchanged: for better and for worse, it hews very closely to the original Diamond and Pearl games, without even taking much from Platinum. Other than a few minor details like easier HMs, gym rematches, fairy types, and battle speed (which isn't saying much, considering the originals were slower than a Sassy Shuckle with a Lagging Tail), it remains not far removed from the original games it remade. The contest change does still irritate me a bit, though; I liked the appeals stage in Gen 3 and 4, and I liked that it had been kept in ORAS. Ultimately, what you saw then is more or less what you get. If you have DPPt from Gen 4 (legally or otherwise), you won't miss much by sticking with the DS. If you want all of the Pokemon from Gen 4 or earlier on the Switch, if you missed Gen 4 and don't wish to emulate, or if you just want to see them in shiny 3D without a Wii and Battle Revolution, BDSP might be a viable option.