Nice
Very nice concept.
I think you tried to make a tower game that offered a lot of alternative ways to finish and initially it looks like you accomplished that. However, it really is frustrating that there is no option to "win". I have a feeling you were going for that but why not just include that gameplay option? A lot of people would be (and looks like, are) frustrated with inevitable defeat. A level based version would also be a good warmup for the never-ending play. Also, if you had a (maybe unlockable) "a lot of money" option, people would try out stuff without playing through a 100 rounds and realizing they missed something essential.
Finally, I can see how the vast maps seem to offer infinite gameplay and infinite options, but in reality they don't. There are certain ways that players decide to play in and they apply that according to each map's design. What I'm saying is that while the options seem limitless, if someone resets the game and designs the same stuff over and over again, then that's not really open ended play. I didn't explain that well but hope you got what I mean. I can't think of any solutions to that without altering the basics of your game.
These were just things I thought could be improved, don't think i'm bashing in any sort of way. I quite like defense games would kill to a sequel to this. Good luck!