It's fun because it's different.
Kirby's "stylus only because remember the DS has that" game.
Also that odd type of game where finishing requires all/most of the collectables (tho this isn't rare for Kirby I guess)

Main gameplay is cool and all but those side games cheffs kiss better than some main game levels. Especially "Strongest Sword" if only for the music

Controlling and throwing multiple Kirbys at the same time is pretty fun at first and each level is unique while using very well the new gimmick, unfortunately, later on the levels get waaaaaaaaay too long for their own good which makes them quite tiring even with it's amount of creativity, the lack of checkpoints/lives also makes this game a lot more punishing than it should be, and the game only warning you that the final world requires you to get all the Rainbow Medals almost at the end of it was a big slap in the face and made me lose interest in beating it, the gameplay is just too simple to really hold my interest in a game as excessively large as this one.

This game has quite possibly one of the best collections of minigames in the franchise, though, not only they are very varied and fun, but some of them are very complete, like Strato Patrol EOS, which is a small shooter 'em up that includes its own levels and bosses, without mentioning the amount of fan service that goes even far enough to include characters from Kirby Right Back at Ya, the sub-games are the only thing that is really avoiding this game from getting a mid/10.

Ohhhhh this one hurts. I wish I liked this more than I did, I really really do. I know a lot of people really like Mass Attack. There are things I really like about it myself. The sub-games are great and wildly inventive. This is one of the first times Kirby went all-in on its random lore callbacks, and it's particularly audacious here with its anime cameos. There's a certain brazen moxie to calling the big bad "DEATH GOD" - not that Kirby's any stranger to baddies like DEATH GOD, but usually it's a bit more subtle about it. The Birdees actually go through a character arc, which is WILD for a throwaway supporting character in a Kirby game. There are a few really cool stage concepts, like the first ring of Dedede Resort and the vehicle-oriented stages in Volcano Valley.

But good grief, is the actual experience of playing the game miserable. I suspect a big part of it was my emulator setup, but I don't think that's it in its entirety. The actual action of the game is flinging Kirbies around and guiding them from point A to point B, but the little guys are so hard to even aim correctly, nevermind micro-manage. So many things can go wrong during normal play, and then the game introduces things like those eggs you have to protect that require precision gameplay in a game ill-suited for it, or all those sub-bosses (especially Great Gear, King Eelongo, and Steelsnapper) that exist just to waste the player's time. That the game expects NO DAMAGE RUNS in this game for 100% completion is insanely cruel, but at least that's just for completionists or folks who really got into it. You don't need to master the game to see the ending, right?

Well, you kinda do! See, the game presents itself as having alternative paths, where each level is split into rings of stages, and only some Stages need to be cleared to reach the boss. That's a neat concept, but access to the next ring is gated behind specific stages, so there's no reason to varying your route. On top of that, the last level in the game requires that every Rainbow Medal be collected. Since there's one Rainbow Medal in every stage, you're just gonna have to play all of them. Furthermore, you need a certain amount of Kirbies to access every stage, and if you don't have enough, you have no choice but to grind out more Kirbies in a previous stage. And you have to EARN those Kirbies, they're not just hanging around waiting for you. Each Kirby essentially requires a 1-Up's worth of work, so you can't just duck into a stage and nab what you need, you're essentially playing out lengthy stages over in their entirety if you can't pass muster. So you might think of stages in earlier levels, where you're relying on fewer fiddly mechanics that'll mill out your Kirbies, but nope - every time you switch levels, before you've beaten the penultimate level's boss, you lose ALL BUT ONE Kirby for your efforts.

It's a striking contrast with Kirby's MO; even earlier games in the series with strict requirements, like 2 and 3, allow for a free, casual, full-ish experience of the game, almost never limiting progress in a given stage to that in another. I like it when Kirby games have bite and challenge the player, but so much of this is just tedium and busywork in a game where moment-to-moment gameplay is either exhausting or mindless (the opposite side of the coin to all the above is that when you have a full team, you mow through enemies quickly - but its it really a reward to have to wait around less? And anyway, so much time is spent trying to keep defeated Kirbies' spirits from flying away, so... more busywork). I'm simply not having fun for the majority of the experience, and I feel bad about that.