i had a flick through the robert graves greek myths book... it's probably a pretty good intro, and it's definitely comprehensive, but there's no fizz to it at all, it's very dry in the way it's written, like reading a dictionary or encyclopedia. i suppose that's what it is, so it's perhaps wrong to criticise it for being that. i've much preferred ovid's metamorphoses, although this is obvs roman, not greek, but there's considerable overlap between greek and roman myths in that the roman ones are using the same source material, doing new spins etc. but having said that, it's also hard to read, cos its so of its time, you have to get into it, give it time, and i've left it now, so the thought of going back to it is not so enticing. but once you get into the rhythm, it's pretty enjoyable.
maybe just read the odyssey or the iliad? whatever decent translation you can find?