Released in 2018, this was the first Kirby game for the Nintendo Switch, but certainly not the last.

Also, this is a mainline game, which means you have all the basic elements from the franchise: Multiple abilities, platforming, Whispy Woods as the first boss, and all the good stuff. However, this time the gimmick is that you can turn enemies into allies, so most of the time you will play with three NPCs (or players) helping you.
To take advantage of that, most levels have some puzzle that needs a specific combination of abilities, like stone+psi, or blade+water. Thankfully, they put enemies with these abilities throughout the level so you don't have to go to previous stages to get them, which is appreciated and avoids having to repeat a level just because you couldn't do a puzzle.

The bosses also take into account that there are four characters at once, so they are chaotic and fill the screen with attacks, which is fun at first, until you realize the best strategy is to protect yourself while the NPCs do all the job. Also, the final bosses are so chaotic and full of special effects that the Switch starts lagging during the battle, which is funny because you wouldn't expect a Kirby game to be so demanding for the console.
Aside from the main mode, you have two minigames that you will probably play for 2 minutes just to get 100% completion, Guest Star ???? Star Allies Go!, where you play an abridged version of the story mode with a random character instead of Kirby (similar to Helper to Hero and Meta Knightmare Returns from previous games), the classic arena, and Heroes in Another Dimension, which is like a post-game story that happens after the main events and was added through a later update. You will complete all of them in like a week, so don't expect anything like Kirby Super Star.

And, to be honest... There isn't much to say about the game. It isn't bad by any means, but it's pretty middle-of-the-road for the franchise. The gimmick doesn't change the gameplay that much and makes the game so easy that you will have more than 100 lives when you arrive at the final boss, the story is interesting to read in summary, but not so much in-game, where the best parts are the boss descriptions from the arena mode in the hardest difficulty, something you will do after doing all the other content.
The level design is generic and feels like a downgrade after Planet Robobot, and if you are familiar with the franchise, you won't get anything new from Star Allies. Considering this was released a year after Breath Of The Wild and Mario Oddysey, it feels underwhelming, like they were working so hard in Forgotten Land that they forgot to add more substance to this game.

In conclusion, this is far from the best Kirby game, but if you are a fan of the franchise and enjoy the classic formula without any major changes, I'm sure you'll enjoy it.