The Obvious: JRPGs
The less-so: Educational games... Yeah, the Wii and DS are saturated with them, but with Bluray, they could honestly hold hours of high def video and just go crazy with content, and if it's not 3d heavy, it wouldn't take that high of an investment... As long as those don't replace real games, I mean.
Horror... I mean, ya know, good horror that's properly optimized for the PS3... With AitD getting pushed back for us... It's a dry time for horror fans.
Those simple concept games that just make you sit back and say "Wow", like Shadow of the Colossus... Guess that's not a genre, but...
Dance Games... Ok, so really only DDR, but why is it on every system but the PS3? Oh, right, Singstar trumped Karaoke Revolution, and the Bemani division is angry at Sony... Guess Konami should have been more international minded with Karaoke Revolution... Still... I hope they make a PS3 DDR, I want DDR with downloadable songs like the Xbox has.