I've no idea of his expertise as a poker player, but I have followed his backgammon books.

He is a good writer. His BG books are entertaining and well worth reading. I believe there was some controversy over the 1st editions of his Advanced Backgammon books.

After computers got good enough, somebody went back and analysed the problems and found about 25% of the solutions were wrong. Apparently Robertie was pretty pissed and threatened to sue for beach of copyright when the analysis was put on the web.