In terms of a standalone game? It's wonderful. Great story, fun mechanics, plenty of stuff to do. A little on the easier side as the EXP scaling is a bit broken, but that's why you just train even more Pokémon. People forget you don't have to stick with the same six for the whole game...
In terms of a remake? A little lazy. We've seen how a remake should be done with HeartGold/SoulSilver and FireRed/LeafGreen. Those games mimic what their original counterparts did, improved it, and then added a whole bunch of new features to make it even more than just a remake.
BDSP faithfully recreates Diamond/Pearl in a refreshing format, but fails to go to the lengths Pokémon games have in the past. Yes, it revamps some things and adds a couple features, but mechanically it isn't too different from Diamond/Pearl. Contests, imo, have even been gutted in these remakes.
Overall, it's a good game but could definitely have been a whole lot better.