Robert is with us to make sure we don't sell Penny Arcade again, that is his main purpose, but he is also Gabe's Splinter Cell partner. It's gotten to some weird level with those two, they have a pair of neon green elastic bracelets to signify their unconventional union and everything.
Japanese RPGs are his genre of choice, they appeal to the math major in him, and it is no doubt the numerical symmetries and relationships that appeal to him in puzzle games as well: he has refined a Greater Theory of Lumines (seriously, he drew diagrams) that allowed him to "flip" the game and earn the final bonus song, like so:
I play games to enter a trance state and experience other lives, he plays them to defeat the designer of the game by proxy. That's a significant distinction.