Top critical review
It's an OK port from 3DS with no improvements. Was not worth the time.
Reviewed in Australia on 30 November 2021
I'd like to start by saying I played all Pokemon games from gen3 to gen8 including sword&shield. I collected every single shiny Pokemon in Pokemon Home. I just sank 600 hours into this Shining Pearl. I believe I can speak with some experience here. This game offers nothing new, no improvements, no interesting mechanics, no new items, no new Pokemons, everything in this game is available in Sword&Shield.
Pokemons: this game only has gen1-4 pokemons, does not have all gen 4 mythical pokemons and is not compatible with Pokemon Home.
Performance: it is a port from the old 3DS game with better graphics. But the same bugs remain, ie. only 2 persons allowed per union room, makes it harder to match with your trade partner and easier for kids to prank you online. Bike mode is just as confusing. The 3DS touch pad with 20 apps has only 1 toggle, if you miss the one you want, you have to toggle right from the beginning. Copious amount of duplication bugs/glitches.
Story: its the same Diamond&Pearl story with nothing more. No Shaymin quest, no darkrai quest, and NO Arceus. Which means it does not include improvements from 3DS Platinum.
The mechanics: omg, whoever thought making all TM moves consumables was a good idea should be fired. There are about 10 TMs you only get 1 copy of and can not be bought anywhere else, if you use them on a bad Pokemon, that's it, no more TM 46 for you.
The grand underground/Ramanas Park: underground is a repetitive digging simulator, it was alright the first couple of digs, then it gets repetitive and tiresome, but you need 2 hours of digging for 1 myth shard, and 9 shards for 1 legendary Pokemon, you do the math on how repetitive it is. At least in Sword&Shield you get to fight boss battles and watch other people with their flashy legendaries, in this game it's just hammer and chisel for days.
Competitive play: if you are a competitive Pokemon fan, bad news for you, no assault vest, no eviolite, no weakness policy, no adrenaline orb etc. Also no new moves such as burning jealousy or rising voltage etc. Also no mega forms, no dynamax, no Z-moves. Anything that makes competitive play interesting is not in this game.
In conclusion. This is a huge step back from Sword&Shield, if you want to enjoy gen8 please play Sword&Shield, otherwise Sun&Moon is the last one with national dex. Steer clear from Brilliant Diamond &Shining Pearl