Definitely Kirby Super Star Ultra

This.. so much this.

No offense, but how the hell can you NOT have the one Kirby game that truly defined the series?

Kirby's Adventure, on NES.

The GBA remake is nice, but the NES original is, IMO, still the best Kirby game. It was amazing for what it accomplished on NES hardware, it was a huge hit late in the system's life, and it is the game that established Kirby's power-absorbing ability. Kirby's Dreamland on GB is a good game. But it's basically Yoshi, you suck up, and spit out, or swallow, enemies. It was Adventure on NES that brought in the power up concept. I remember first renting the game and being blown away. Having already played many of the Mega Man games, I was very familiar with getting powers from bosses. But Kirby upped that in various ways, by not only letting you take powers from enemies within a given level, but allowing you to discard and switch to another power in the same level. And the sheer magnitude of power ups, for an NES game or any game at that time, really, was fairly ambitious and unheard of, as there were close to 20 different powers you could get.

Later games certainly did creative and fun things with the formula, and I can certainly see, graphics and otherwise, how people could make the argument that other Kirby titles are better. In all honesty, I've liked and enjoyed MOST of the "main series" Kirby games, myself.

But for my money, Kirby's Adventure is still the best. And it should have been on the list.

I recently played Kirbys nightmare in dreamland and i thought it was not mindblowing, it was fun but i would give it like a 6.5 out of 10, im sorry xD