I was prompted to make this when out of the blue my physical copy of Shantae and the Seven Sirens arrived today!
And here I am a year and a half later FINALLY getting around to this in my backlog.
Verdict: Definitely a mixed bag.
I enjoyed the engine in Half Genie Hero so the moment-to-moment gameplay was good, reducing the animal transformations to individual moves instead of actual new forms that require stopping the action to first perform a dance is preferable to the old way, even if something is lost from the charm of the OG titles. Wasn't a huge fan of the four ACTUAL dances you get in the game as they are rarely anything more than 'blue key for blue door' abilities, and annoyingly any and all rooms where you need to use them give you a blatant visual indicator. The refresh dance is probably the only one that had practical use, but even then trying to use any of them forces you to stop what you're doing.
The game seems to have its best ideas crammed at the start and the dungeons feel like they decrease in quality as the game goes on, hitting the absolute nadir in the Squid Pit which was just a series of kill rooms on a timer followed by the absolute worst boss in the game. Octo Siren felt like they ran out of time and just needed to make one more boss so they went with 'Simon Says but without the part where you see the pattern first', come on Shantae team you can do better than that. It picked up a bit for the last dungeon, even if it was just a linear gauntlet rather than a labyrinth, and the final boss was memorable at least, if not super challenging.
Writing was all over the place but par for the course for the series. Voice acting was much more miss than hit more often than not (Lobster Siren's squeaking was probably supposed to be cute and charming but personally I found it to become insufferable really quick).
I liked the little animated movies that played throughout, made it feel like a platformer from the PSX era back when adding movies was something new and novel.
One thing that really soured me on the game, though, was trying to get 100% completion. I eventually stopped when I realized one Heart Squid was locked behind that Dance Parlor game, specifically breaking all targets without missing once, which was just an inexplicably bad decision. Even worse ending screens are locked behind 100% completion. Just... why. I'll cut my losses there and just look up the pics online (will they have characters in swimsuits and the like? I bet they just might!).
So all 'n all, still a fun game and I enjoyed it more often than not, but not the most memorable entry in the series. If an when we get Shantae 6 I hope they bring back their A game.