In a sense, I feel like they are underrated in that people hate them a bit too much. I didn't think they were amazing Pokemon games, but I did feel like they were entertaining enough. I have a few complaints, but most of that deals with the glitches (though I think those are overstated), the enormous patch after how the game was initially shopped, and on a personal note, the friendship not maxing before 255, making the hax benefits sort of just happen more often over time. I actually used bitter herbs in the Elite 4 just to keep the battles a bit more even over time. A few other minor nitpicks to note, is that you can't decorate a Secret Base like you could in ORAS, and good luck finding the Pixie Plate. Besides that, despite the few changes the game makes, I thought they were good inclusions, like the Grand Underground caverns, the clothing shop, and Ramanas Park. Post game especially lets you dive into a wealth of more content, which was true for the DS games, and it's true here as well. What is different in these titles is that the QoL is so much better. No more 12 seconds for watching Lv. 100 Blissey's health drain, and you don't have to stick lame HMs on Pokemon to get everywhere. I didn't mind it so much in ORAS, but because Sinnoh feels scattered in its HM usage, you have to use them in all different places.
I guess the other thing I'll note is that Sinnoh is one of my least favorite regions. BDSP were fun enough to warrant the revisit, but a simple remake doesn't make my least favorite region my favorite all of a sudden. Legends Arceus re-imagined the region in Hisui, which was significantly different, but familiar.