Which theme did you end up using?
Tower Defense

Any obstacles you found while working that were hard to overcome?
A number of gamebreaking bugs, learning how to do A* pathfinding

Anything you had to ultimately cut from the game due to time or lack of knowledge?
branched upgrade paths, death animations, a 5th tower, optimization

Anything really cool or interesting that you learned?
I learned A* which was a lot of fun

Do you think you will continue this project?
I don't think I'll continue this project as it's rather inefficient and has become unwieldy (just take a look at shapeDefinitions.pde if you want an example)