Love the sound design, such lovely textures! I also liked the overall structure, the gradual build up in timbral complexity, seemed paced very well to me.
Personally I didn't miss a melody, I thought it was fine without. Perhaps it could use a bit more variety of some kind; if not a melody then perhaps more harmonies/chords, or alternatively more drastic changes in the sonic space...however I think it still works without these things as a more static background piece.