Sorry killertitan135, this is not from the same makers as Kingdom Rush. That was by Ironhide Studios. Don't jump to conclusions.
Though at first I thought it was another Kingdom Rush clone because many design aspects bear a strong similarity to Kingdom Rush including the title screen, map screen, victory screen, and level layouts. As it turns out, this isn't even Tower Defense but rather an interesting take on lane-based strategy games which I think originated with Krin's Tainted Kingdom, the sequel to which I'm still waiting for.
This game can be very easy if you buy the right upgrades and very difficult if you buy the wrong ones. I first bought the cavalry and that turned out to be a mistake because it's the most expensive unit in the game and practically useless. I was thinking I could rush the lanes and get my unit through before enemies show up, but they show up too quickly so it doesn't work. So basically the cavalry is only useful for getting reinforcements to the front lines quickly, which is seldom needed if at all. Upgrading old units is better than buying new ones because then you get more powerful units for the same cheap price. But even better are the spells. Having spells regenerate while you fight is like having an extra source of income, and you can kill powerful units with them early on so you can gain the upper hand money-wise right away.
Starting with level 9 the space bar stopped working to switch lanes. Maybe you forgot to program in the order that the lines cycle through. Also, the last few levels all had the same enemies. Maybe put in a big boss enemy for the last level.
Looks like the lane change buttons can be blocked by units. Should make sure buttons are always on the top layer. Or at least set mouseEnabled and mouseChildren to false for every layer above the units. And it looks like there's some difficulty picking up coins as well. Maybe instead of using a ROLL_OVER event you should just check each coin to see if it's close to the mouse and then have the coins drift towards the mouse and get picked up. That way you could pick up coins that are behind other layers. Also, there should be a magnet upgrade to attract more coins from further away.