reosonable
its prety good it could do with some upgrades and you should have to unlock some creatures but the towers should get built over time instead of at the beggining of the level. if you made a second one it might be oustanding if you take the reviews to acount
Better
It could be better, but it's really good, good concept, maybe some of the graphics can be reviewed. I'm thinking here about the buttons for the units and the overall graphic identity, i think it's not a bad graphic design but maybe some hover would clearly help the user seeing things. As well as your button to add units ("Let it out"), should be right under the choosing unit arrows, or vice versa. Those small details would really better the overall design of your game. Might also want to reduce difficulty on level 4, it's pretty hard as it is right now. I'd expect that kind of difficulty for a level 10-ish
Too hard
I love challenges but this gets tiresome and kind of frustating easely. May be if you could get achievements and get more money or upgrade your little guys in a different way...
Maybe not as a stand-alone
I think every tower defense games need this as extra mode, double the fun.
I know this is an older game but....
This could be great, add achievements that help make the game easier (level 4's a bit hard for most people). Like deploy a total of 100 units in one game and win to start out with 200 more cash. Things like that would make the game much more addictive.
On a side note, when this first came out it was a great idea and a great game.