It kinda pains me to say I wouldn't recommend it, especially since I got it from a friend. (I'm sorry, bud. Thanks all the same!)
Next to the other Shantae games I've played, this one's pretty meh.
The stories in these games are never extraordinary, but this one feels particularly phoned in. There's not nearly as much character to it as there is in the rest of the series.
The transformations and dances feel pretty underwhelming as far as mechanics go. Restoration is the one that gets spammed. Seer mostly just finds pocket change. Quake is alright. The lightning one is just eh.
Hiking across the map gets to be a bit of a slog. If you're just going for squids, it's probably fine. If you're going for nuggets, I offer my condolences.
I'm glad they gave the indicators for where to use the dances, it certainly makes finding things easier, but at the same time, I can't help but feel like it shouldn't have been designed in such a way as to need them. I couldn't imagine nugget hunting without them. I probably wouldn't have bothered.
I played on Definitive mode. It definitely had some challenge to it, and it felt pretty quick, so on those fronts it accomplished its stated goals. That said, it feels like it's in a weird spot where it's very easy to get health back and also very easy to take a whole bunch of damage. Something definitely feels off there, but maybe it's just me.
The cards seem like a bit of a nothingburger. Very few of them do things that matter. I used hair whip damage up and magic regen from the moments I got them until the end of the game and essentially never swapped.
Some of the bosses are pretty disappointing. Octo Siren and the Empress Siren's final form come to mind in the sense that the former is a guessing game and the latter is basically just fighting an art asset.
If you're a huge Shantae fan or a metroidvania lover, you'll probably get at least something out of this game. I certainly didn't hate it, it just feels like a cool 5/10.
If you're gonna play a Shantae game, I'd recommend the others. If you're dead set on this one, get it on sale.

It's an OKAY game, story focused but still a fun metroidvania. I 100% it in 3 playthroughs in different modes, didn't get bored at least. FUSION! DANCE!

imo rule breaker most fun gamemode, beginner is too op and forgiving, definitive for the authentic experience