RTS games. Actually the only quality hand-held RTS game I had seen on current-gen hand-helds is not even out yet... yes, Im talking about Galaxy's End. Except that game I dont even know if I had seen any, except some niche Japanese ones. Shooters are lacking to. Yes, the PSP has the two Syphon Filter, Medal of Honor and SOCCOM games ( well actually 3 SOCCOM and Syphon Filter games but one is a TBT game and the other is DLC only ), and the DS has MPH and Dementium the Ward and both systems have at least a half dozen mediocre shooters to, but its still not enough IMO.
For beat'em ups Chains of Olympus was great for the PSP, and Im certain that Capcom wouldent disapoint with a Devil May Cry game neither ( Dance of Sparda anyone?), but again, I would definatly want more. Ninja Gaiden DS was great, but I would want one for the PSP to, because it just fits the system more. For the DS I would like to see more 3D platformers, because its more then capable to handle them ( as SM64DS proved it ).
And as a final idea I would like to add horror/survivor games to. resident Evil DS, Silent Hill Origins and Dementium proved that both systems can handle games that are capable to spook us out, so why dont we see more of them? I know that sales might not be stellar, but IMO the market is still there and pretty open, and it might be a great financial bet to