>Music and animation that fit the mood of the series or are representative of the series in some way
>Good quality, OP-specific animation
>Animation and music are at least somewhat synchronized
First point is especially important. I was interested in Gangsta only because of the OP, which suggested an over the top, fast paced crime action show. Meanwhile, show turned out to be slow with barely any action. On the other hand you have shows like OPM and Re: Cutie Honey, and the OP fits them like a glove.