Your terrain is... Simple. There is nothing really eye catching. As a first means of improvement, I would suggest redoing much of it, try something that havnt been tried before, however, this is more of a wish thought I suppose, seeing as you most sertainly dont want to redo the entire thing. And as leet.firefox pointed out, it needs more tile variety in some spots, while in other spots you need to replace them, since when did grass grow under water? Also, I would try to avoid using blizzard cliffs if I were you, of course I wont talk too much about it as it is a playable map, but done in the right way; it looks ten times better without blizzard cliffs.
Appart from that, as some other small pointers, I am not too huge of a fan of using that Underground tile in the setting you are using it in, and I would strongly suggest that you got yourself some more imports. Mostly I would suggest finding a better model to use than the normal Shrub model, look through the UTM, the models there nearly doesnt take any space ^^