Neat game, I like tower defence games :D
It's a bit rough to place things when the store menu pops up though because it covers up the track.
And to upgrade units I've got to dropdown the store so I can see how much cash I've got.
Greater clarity between where I can place units and the path of the monsters would improve things quite a bit.
Having a couple of clumped together swordsmen mow down enemies felt pretty good while the defence lasted.
Nice job :D