Downright awful.
Crap pathing system (I can put the first and last in the middle, the others at the edges of the screen and blaze through the game), no price scaling on the units and upgrades (although the prices randomly go up or down by a dollar for whatever reason), extreme mode just gives you more enemies to defeat and makes it nearly impossible to actually kill some to get new tower or upgrades due to the crap autotarget, units are uninspired and lacking in versatility, the missile unit is downright broken. I think I got up to level 50 by leaving it running and not doing anything with a dozen missiles or so.
If you want to make a defence game, play some first so you know what you should be making.
Graphics: 3/10
Sound: 1/10 (Music toggle is nice, but give me a sound toggle already, your sound effects are abysmal)
Gameplay: 1/10
Fun Factor: 3/10 (I'll give you a 3 because I at least kept me busy for a while to figure out in how many ways I could break your gameplay.)
Why the hell did this get front page?