I decided to make a Roguelike-Tactical-Deckbuilding-Shmup:

You plan what your space ship will do during the next 10 seconds. For that you get some manouvers at the beginning of eeach round, which are drawn from a deck. The goal is to eliminate all enemies (or at least survive the wave). Ideally you will be able to refine your deck and upgrade the ship between waves. However from my LD-experience I can predict that only half of the ideas will be done in the end :D