One of the my favorite games was Xenon 2 Megablast.  It’s a vertical-scrolling space-shooter game, the best-looking on the PC that came out in the late 80s, best looking VGA shooter at that time.   It has five (or six, can’t remember) stages , each looks completely different from the others.  The enemies are varied and the weapon-power ups (bought from a creepy alien store at the end on each stage) are lots of fun.

The Bitmap Brothers has a new version, Xenon 2000, that can be downloaded for free at http://www.bitmap-brothers.co.uk/features/xenon2000/index.htm.