Beautiful level design, a wide variety of powers and abilities, and cute, funny bosses. Kirby Super Star had all these features as well, of course, co-op play. I've always loved platformers, so it's no surprise that I love KSS. I don't know what it is exactly about Kirby games that appeal to me so much. They don't tell a complex story, and they definitely aren't challenging. Somehow I always have a great time playing them anyways, and I always look forward to the next installment.
What makes Kirby Super Star the king of the Kirby games? The co-op play! Unlike a lot of other co-op platformers, the second player doesn't just tag along. (I'm looking at you, Tails.) While Kirby is in more control, the helper gets more variety since powers transform him into completely different people. Kirby Super Star is especially cool because it's not even split-screen; everything takes place in a single space.
While I did play KSS when it was new, my fondest memories are of replaying it in high school in the early 2000s with my friend, William. I don't think we ever got all the way through it. We'd always end up restarting. And now, Nintendo's brought it back with Kirby Super Star Ultra for the DS. And again, I started playing it with William. Unlike online games that always seem a little less fun, KSSU let's us sit together, talking and enjoying our co-op experience in person. Oh, and I almost forgot: Kirby Super Star Ultra let's you play as Meta Knight!