Interesting
I love the idea.
However, I think it was a little poorly implemented for a couple of reasons:
1) at the end, you have all the towers, which means theres very little purpose in the tech tree idea. Wouldnt it be better for the player to have to choose, rather than have everything unlocked?
2) the towers seem to have very little basis on what came before. blue + yellow make green but how do a frost and a money tower make a shockwave tower? It doesnt make sense but this is probably pettiness on my part.
3) The purple towers are essential. That -10 armour is huge and Im sorry, but I dont like the way that 1 tower is neccesary to do the game. Makes the game rather linear and removes alot of replay value.
All in all though, it was a great little game. Could use an accelerate button but you know that. And it could use a quality button as i got a fair bit of lag towards the end.
However, Im eagerly looking forward to spectrum TD 2.