Summary
Man this was fun back in its day...
The Good
I remember playing this when I was about 6 or 7 years old on my dad's XT. I was awesome at this game, once reaching level 200-something (the low 200s) after playing for over 4 hours non-stop. When I lost my last life I immediately went to sleep! I wouldn't exactly call this a great game, but it was definitely fun, and if I ever get a working XT or similar computer I'll play it again (I've got over 200 games made in the early to mid 80s).
The Bad
This game literally takes forever to finish. I played to level 200 and it wasn't done, and since there are no saves, this takes a long time!
The Bottom Line
Cosmic Crusader is similar to Galaxian, but adds the twist of having a temporary shield. It's best to save the shields for later levels because they get REALLY hard. Then again, once you're past level 50 they're ALL hard.