Great game and a nice spin on the tower defense genre. A few comments:
1. The tooltip UI for the units can be better placed/scaled such that it doesn't obscure the gameplay.
2. Shortcut keys (1, 2, 3 etc.) for the units available would be nice.
3. Difficulty spike from Level 1 to 2 is a bit steep... but it could just be me.
Not too shabby for 12 sleep-deprived students.