Mine is probably an unpopular pick, but I'm going to go with Kirby 64.
The ability to combine powers has been my favorite aspect of any Kirby game in the series (in other games if you swallow two enemies at once, you just get to pick a random power). Whether it was a standard bomb power, double stone, or dual light-saber, finding and experimenting powers was the highlight of the series.
Of course, there are duds like spike-spark or stone-bomb (how was I supposed to know that down on the dpad would activate a hardhat?), but there are enough cool and weird powers to cancel it out (refrigerator kirby anyone?). Also, the segments with Kirby's buddies were a good change of pace (with the exception of Adeline box segments, those were annoyingly frustrating).
It's also the only Kirby game I felt truly rewarded after 100%ing it.
Finding all those crystal shards without a guide; challenging, but rewarding.
