I’m calling this one done. Will post a post-mortem (and food!) later.
(1) You’ll need at least the XNA redistributable to run it. Also, a decent 3D card (anything from the last 4-5 years. Technically Intel GMA should work too!)
Download: XNA redist
(2) During gameplay, Z fires spread shots, X fires laser, Z+X fire missiles.
(3) The wall circles block enemy bullets of the same colour. Move into the circles and shoot to change the colours.
(4) When the wall is up and running, C uses your super attack (+ temporary invincibility). When it is offline, C summons it at the cost of one bomb.
(5) When the game finishes, please press Esc to exit. Didn’t have time to test and debug go-back-to-main-menu, even though the code is half-finished.
If it doesn’t run even after installing the XNA redistributable, please consult my contest page: