Ok I played your map alone so I haven't tested everything:
- Terrain could be better filled with doodads and destructibles.
- Creeps are a bit boring, they can only attack. Make them use abilities like frenzy or something like that, figure something out.
+ Nice icons so far, they look good together.
+ A nice choice of models (but don't make the rifleman model so dark).
+ I like the bullet system.
x Add more of those bosses like dragons.
x Try to make more abilities triggered, like your flare ability.
x It still lacks sounds, add some gun firing sounds when your attack a creep or unit. Maybe also add some music, one tune is enough I think.