lol "Dan B" (you have the same name as a VGM composer, how coincidental )
1. It has a strong melody and memorable compositional aspects. The melodies were all they had back then, which is why they were so frikkin awesome.
2. VGM can't really be defined as anything. There are composers that mix jazz and electronica (and maybe chiptune stuff) together, but there are also composers who make that ridiculously generic big percussion four note string detaches with choir in the background film type "epic" music. The former usually has more interesting melodies, so I like that better, but there are also ambient stuff, rock, pop, any genre you can think of appearing in games. There's really no definition as far as genre. Main melodies can't even be the definition, because there are composers that do what I said above: copy "epic" film music that doesn't have a moving melody.
3. Melodies on an instrumental level need to be paid attention to of instead of lyrics. Compositional aspects are much more important.