They're probably the most drastic reinvention of the Pokémon formula (barring Arceus but that seems to exist in its own vacuum) and there's deffo a core of something quite compelling in there. It has been a while since I've played, but I remember having fun with it, and co-opping even if it's nothing more than just sharing a game world, was also quite fun.
I'd say if you can get it cheap, give it a shot, but it is really badly baked and there were some very very bad bugs and performance back when I was playing, and I don't think they are worth full price.