This game was a created in a team of 5. Actually, it was the same team as Planetary Face-Off. The total time to completion was also only two weeks. We liked Flixel, so we used it again. The time, we made a bullet-hell shooter. The interesting mechanic here is that the player accumulates resources during play that they can use to summon minion units. Each minion has a specific cost and purpose, so there's a bit of strategy.
Picking a familiar set of tools allowed us to be more ambitious, and that shows in the extensibility of the game. Adding new enemies, new bosses, and new attack patterns is a breeze, and the core mechanics lend themselves well to an upgrade system.