Incredibly poignant pic! It has a little of the patronizing quality of the original, with Harry declaring how he can 'redeem' the poor potions seller, but there is an element of pathos in how far Severus has fallen from his canon role. Ron actually looks like he is the more sympathetic of the boys here.
The colors are intense, and the lines and shading (particularly that of the faces) are concise, but very effective in delineating attitude. Severus' rendering is especially lustrous: rich, deep, and vivid.