I would love to see GTA on WP. Honestly I'm pretty happy with what is already there, I would like consistent support more inline with the other two players in the field. I would also like to have Modern Combat 5 come to WP.
Also, I would love for Candy Crush to come to WP. Personally, I have no interest in playing it, but I feel like it's one of the key missing apps from the platform. I could have sold at least 2 WPs to a couple, but the moment they found out two apps were missing (CCS and Instagram), their attitude changed instantly. For the growth of the platform, CCS is probably the one game I want most.