see colon said:technicly any videogame RPG isn't an RPG at all, since you aren't really playing a role. so unless you dress up in a costume, whack your friends with nerf swords (or the real thing), and hurl foam balls at them (lightnight bolt, lightning bolt) while speaking in a funny accent while you're playing final fantasy, it's not role playing.
i consider zelda and diablo to be in the same genre.
I'm a role player with 10 years experience, so I know what a RPG really is, but RPG applied to video games just means something different, I tend to use the term 'CRPG', with C meaning Computer to talk about them, just forgot to do so.
Anyway I disagree about putting Diablo & Zelda in the same genre.