A mixed bag. The 5-Star reviews over-exaggerate its good qualities. Don't play as your first Kirby game.
This is, by a long shot, the easiest and most bland Kirby you can play... and the series was already known for being easy. The levels are generic, the puzzles thoughtless, and the bosses die in seconds. The game plays itself for you.
The free DLC helps some, but doesn't change any of these problems. It just adds some characters & a tough (short) post-game to say "look, we have difficulty, stop complaining!"
Kirby's always been about appealing to a wide audience through easy but fun and engaging gameplay. Star Allies betrays this formula by removing most engagement and prioritizing pre-schoolers as the target audience (confirmed in developer interview).
This game is best for fans, kids and people that just want a simple, turn-off-your-brain type of game to pass the time with.