Aww! I'm not the biggest fan of Thranduil, but I always adore art of parents and their children, especially with characters that aren't remotely 'soft' as parenthood is that rare glimpse of their barely-seen soft side.
This is lovely, and while Legolas and his father look VERY similar, they do have their own features, and you've done that well here. The biggest difference I think is in the eyes. Thranduil's are sharper and Legolas' are softer, but no less noble.