Isn't he known for writing really dark Pokemon stories.
If so, let the madman unleash his genius.
You mean dark, edgy and ultraviolent stories? HehehehahahahHAHAHAHA... nope. Not really. If I had one image to describe the tone of Pokemon Adventures it could possibly be this...
From left to right, you have Misty in the orange striped shirt, Ash in the red coat and Brock in the blue coat. After being on so many adventures across the region of Sinnoh, dealing with an army of Bidoofs, staying at a haunted chateau for the night, challenging the Pokemon Contests of Hearthrome City, crying in tears that the three have to go their separate ways. Your reminded that they are still just kids. Eventually you see three together again after venturing into the abyss of the distortion world. You see the three reunited and fist-bumping to each other... but wait a minute. This isn't Misty, Ash and Brock. This is Pearl, Platina and Diamond, characters who share similar traits but can still stand as their own memorable characters. You have Pearl the hyper short-tempered lad (similar to Misty) who acts as the leader and teacher of the group, which makes a lot of sense since he is the son of a Frontier Brain. You have Platina the inexperienced Pokemon trainer who challenges all 8 gyms in order to learn more about Pokemon (similar to Ash) and yet is like a living encyclopedia with almost no experience in this brand new world of Pokemon. Then you have the mellow happy go-lucky Diamond who understands and takes good care of his Pokemon while having amazing cooking skills and a pretty obvious crush on Platina (similar to Brock and his affection for girls), often helping her get back on her feet whenever she feels empty and broken inside.
If I would have to suggest a manga story arc that appeals to the anime Pokemon fan inside of all of us, it would definitely be the Diamond and Pearl/Platinum story arcs. I suppose it's because it not only offers an impressive take on the themes of friendship, hope and change better than any Pokemon medium I've seen, but it also undoubtedly offers the most joyous beautiful scene ever created in the Pokemon series, one that could make you a little teary-eyed of seeing someone's faith in humanity restored. The image I posted in general gives you a good idea on how light-hearted and fun Pokemon Adventures is. Is it dark? Not really. Does it have dark moments? Of course, it is still a mature take on Pokemon but it's nowhere as dark as your Harry Potter or Star Wars.
So why do I say Kusaka is a mad genius? The same way One Piece fans see Oda as a mad genius. He's an awesome storyteller that will blow your mind in the terms of planning and care he's put into his work.