I'm working on a project of mine in the same category as yours.
And i am using terrain in a good way. Nice eyecandy that doesnt affect the gameplay.
You can use foliage and light, aswell as the cool 'Dust - Leaves' effect.
Texture-mixture is also a great idea and improves the whole layout and design by alot.
Design is very important to get your map popular. Eyecandy affects people in a way that makes them like your map.
Custom UI, good terrain, artwork, all of those things are very important in people's eyes.
Of cause a map cant be popular with a good design only. Gameplay and uniqueness is important too.
But as i think your map has quite good gameplay, you should start focus on the terrain.
I hope this has helped you. I wish you good luck in further development and will check back later.