I played Kirby: Planet Robobot and beat it, though I've only played the main story and haven't played all the EX stages or the other modes.
It's pretty awesome. I haven't played any Kirby games after Nightmare in Dreamland so keep that in mind that I don't really know what direction the Kirby franchise has really gone.
First off I noticed a strong Kirby Superstar vibe. Like Superstar you can do lots of different attacks and combos with each ability, and the Jet and Mirror abilities to me feel distinctly Superstar-ish and they hadn't appeared in any other games until this one. There's also some recognizable Superstar sound effects.
The robot suit is fun and you feel really powerful while using it. When it's in use the player can't just fly forever (except in parasol mode) so here, in a Kirby game, you've got more traditional platforming. There are other places that find a way to justify the player not just being able to fly, like the sections that have Kirby holding a battery that he has to carry somewhere. There are whole levels set up around the robot suit bringing in new gameplay, like when it copies the jet it turns into a shooter game (with awesome music), and when it copies the wheel ability it's pretty different as well.
The level design has a lot more puzzles than before! The code cubes thing makes you do all sorts of little challenges and exploration. The puzzles actually have you using abilities, like ice to freeze water to make a bridge for yourself or enemies, and electricity to power something.
The levels are designed a lot around jumping between the foreground and background, which Kirby Triple Deluxe apparently also does, but since I hadn't played that I thought of Virtual Boy Wario Land and Mutant Mudds.
Thoughts for final boss:
Holy crap it's sooooo long, like I had to take down 5 life bars or so. A lot of it was just moving around in a 2D space while avoiding things, which Undertale surprisingly prepared me very well for, and then the last part of it had me spinning the circle pad around super quickly like this was Mario Party or something. It felt pretty epic though and it was really satisfying.