Nice! though I'd recommend changing the title and file name to exclude the word "gradius". It's still a trademark of Konami. Were any of the original gradius sprites used as a base for these?

None of these exactly match anything I could find in the Gradius originals. However I would not be comfortable using the turret, power-up, or player ship. Those three feel to close to their originals to me (Gradius 1). The purple rocks and launch bay in the upper right seem fine (for Gradius any way). The explosion is Gradius like, however it is different and generic enough I believe it would pose no problem either.

I really can't say on anything else. Hope that helps.