It's just for pokemon games, you can't play other gameboy games through it, however, there were rumored other games taht would support gameplay through the device. Or support. I seem to remember "perfect dark" (may be remembering wrong) was originally supposed to use the gameboy camera to put you "in" the game...yeah, I can see a few obvious reasons that didn't happen though.
Oh, and it's only certain pokemon games. If I recall correctly, the first three (red blue and yellow) could be played on the first Pokemon Stadium game, if you wanted to play Gold Silver or Crystal, you had to have Pokemon Stadium 2....I don't remember if the first three could be played on the second pokemon stadium or not, I don't see why not.
I seem to remember some of the Mario "sports" games could transfer stats between them with the transfer pak. (mario Golf?) But as I don't have the 64 game I 've never tired.
My favorite thing with Pokemon on the transfer pak was the "fast forward" function. God it was actually painful to play that game on the gameboy after playing it on the 64

Perfect for turn base game play like Pokemon.
Edited by Video, Wed Mar 9, 2011 3:50 PM.