It's an interesting mix of the two game mechanics! You seem to have implemented several enemy types and weapons, that's a good thing!
Although I must admit it's really difficult to play (it's not easy to concentrate on jumping and placing of the turrets, so I either did one or the other). And I don't really know if I should be avoiding anything in the endless runner. It didn't seem to have any effect so it would be cool to have some more explanation on that. Also I think that what would be great is to have some more feedback from the game. Like for example more in-game effect of the "more ammo" and "increase damage" buttons.
The graphics aren't outstanding ;) but don't come in the way of play and you can always improve that later after you've polished the gameplay.
Anyway it's a cool game. I'm just writing all this because you asked for ways to improve the game ;)