Tips so far? Don't be afraid to be harsh, but take into account this is a HUGE work in progress.

The stock matches well. I think you should work on making the horse 'smoother', it looks like when you cut it out you made a few jagged lines. The horses face blends in with the background, making it look like it is cut off. The hooves are very jagged and not the correct shape. It looks great so far!