I think there's a lot to like in this model. Its probably being marked down for the plain-ness of the horses. Try
1. An ink wash on the mane/tail. The yellow is a bit unnatural anyway, but it is fantasy...
2. Some form of shading on the horses themselves
3. Horse eyes. Dark socket, white then dot in middle.
4. Darker shade in nostrils and mouth.
I liked the banner and the chariot wheels, and the general neat strong colours.