I agree with this. If there's going to be a mythology in a story, it'll more than likely be Greco-Roman mythology if it's coming from the West. Norse is gaining in popularity, though, thanks in no small part to Marvel's interpretations of Thor and Loki.
Greek mythology is one of the most thoroughly-documented and most accessible in terms of its narrative structure and characterizations. Egyptian mythology and Far-Eastern mythologies can be harder for westerners to comprehend since they tend to be a great deal more abstract. Celtic and Scandinavian mythologies, so far as I'm aware, have a lot of troublesome gaps in the lore and can be quite nebulous themselves. That said, I think most fantasy races and tropes come from those mythologies, right? I'd say that makes them more influential than Greek.
To make a long post shorter, I love mythologies in general and hope to write stories in most everyone I'm familiar with, but Greek mythology is the one I best understand and admire. The four short stories I've put up here (plus the ongoing fifth) should be evidence of that 
.
Greek mythology is just so full of drama and big personalities, and as a young writer, I always found myself dissatisfied with most of the interpretations I've seen. As @bakasama25 suggested, the stories tend to twist the personalities of the characters a great deal for poor reasons. I can appreciate altering them if you're changing the stories significantly, a la Disney's Hercules or the more recent Immortals. But we got two Hercules movies in a row a couple years back, and both of them missed pretty much every mark regarding his character.
Are you kidding me? Heracles (they never use the Greek name >_>) was a hard-drinking, musclebound bisexual whose wit rivaled his strength. He killed his music teacher with the man's own lyre. He traveled with Jason and the Argonauts. He once slept with 50 sisters in 50 nights (or, 1 night, depending on the telling). On the dark side, he also murdered his own wife and children with his bare hands because a vengeful goddess hit him with a fit of madness. He has the potential for madcap adventures and heart-wrenching drama, but I've yet to see an adaptation that brings that across. So, I wrote one 
. That one's not ready for the public yet, though.
That's just Heracles. I could go on, but I've rambled long enough for one post x).
