Kirby's Adventure is the largest NES game ever officially released in terms of ROM size, and has a frankly absurd amount of graphics tiles. Just consider all of those required for the copy abilities thumbnails alone and you'll see what I mean. It pulled basically every trick the MMC3 mapper is capable of, and was definitely a masterpiece of the system in the original sense, i.e. it displays astonishing mastery of the mechanics of the Famicom/NES.

What I find more amazing is that the MMC3 isn't one of the mappers that confers any additional sound channels and the American NES didn't support that capability anyway. So the entirety of the game's iconic soundtrack fits within the confines of the NES' two square waves, one triangle wave, one noise channel, and singular PCM channel.

I think ultimately it ran into memory constraints, even with the additional 8 KB provided by the mapper. If you sit back and look at them as a whole, its levels are all quite short. It's still my favorite NES game bar none, though.