I have a little mixed feelings on this game when trying to compare it to other Kirby installments.
Gameplay-wise, I liked Return to Dreamland more. Sure, robobot armor is an interesting concept and is done pretty well, but game still feels kinda unfinished for some reason and autoscroller sections ruined few levels for me. If you never played any Kirby games it will not disappoint you, but if you did, it might.
But it indeed have some strong sides. First things first, its plot. You'll have to complete extra mode and true arena to learn it (or read Kirby wiki), but it is totally worth it.
Then it have an excellent final boss, my favorite up to this day, solid soundtrack and bonus game modes that are a lot of fun to play.
TL;DR: not best Kirby game ever, but still worth playing.