Kirby's Adventure was already awesome enough, especially when you consider the large amount of powers you could copy (UFO was awesome), but the final boss fight where you get to use the Star Rod Really tops it off. Who wouldn't want to battle a boss while flying through space?
Others in the series:
Homerun Bat and Yo-Yo - [link] Dedede's Hammer - [link] Master Sword - [link]
UFO *was* awesome. It was a shame you couldn't keep it once you exited the level though. The Star Rod was pretty cool too. It was nice that you could shoot stars with it and not just have to use it like a sword.