Bilal comes across as much more influenced by Jazz and D influenced by Soul/Funk/R&B. I know Bilal has some of those influences as well but there is a big Jazz element in his music to me and that generally doesn't translate to huge mainstream success even though he is by far the better singer and someone that can vocally hang with anyone. D'Angelo's influences are much more along the lines of what the core fan base of R&B digs...sexy, edgy but relatable. As others have pointed out Bilal is a lot more quirky than D who comes across like the cool ass homie who is really talented but more like your average brotha.