Honest to God...

This work is really amazing.
The composition is nice, well balanced. Maybe the background could have been a bit darked to focus more on the characters.
The colors are great, the blues, purples and blacks work wonderfully together. they create a dark an mysterious atmosphere.
the texture is also very well done, especially on the wings. It's like we could touch those black feathers.
On the characters, the faces are very living, they carry emotions (especially lust <img src="e.deviantart.net/emoticons/w/w…" width="15" height="15" alt="" title=" (Wink)" /> ). the pose is nice and fits to your theme. The anatomy is very good. Maybe the legs of the black angel could have been a little longer and less thin, but that doesn't take from the drawing.
As a conclusion, a really nice work (which reminds me of some of Kaori Yuki's work). The only thing I can really say is keep on the good work.