Hot Take: None of them are bad (some maybe meh but playable) but the series is rarely exceptional. It's kind of the same game over and over like the NSMB series. My reaction to most games are 'yep thats a Kirby game' It's fun but shallow. I love it but not realy wowed by it.
The unique gimmick can spice things up, but it's still all kinda blurs together for me, they never realy drastically change gameplay much. I still enjoy it. I also enjoy NSMB as a whole, its fine just is a little bland at times. Each one also has a gimmick too, aside from U.