I think the majority of the Shantae games have progressively built to be better and better, Shantae: Half-Genie Hero seems to side step from Pirate's Curse formula ( A hybrid of Zelda/Metroid) and dived into being more purely Castlevania like (both Metroidvania and original versions). This honestly took me aback at first, and while the game certainly does warm up well enough, it just doesn't hit the exact highs that Shantae and The Pirate's Curse did.
The main problem with Half Genie Hero is just the lack of content it had going in. A lot of the base game plays as sort of individual levels and then when you backtrack to get more collectables the levels become a little more lackluster. Often the first time you enter new areas something big is going on, or an event is happening, but when you head back to get items or collectibles you missed or may need to progress, there is just half of what was there. It certainly isn't the biggest problem, but it certainly breaks the flow of the game. This is especially concerning with how well the Metroid format of interconnected worlds meant for collectibles, or how contained the dungeons were in the previous games.
While I think Half-Genie Hero still puts the correct steps forward in terms of platforming and the usage of Shantae's forms; the constant backtracking and nature of this game's story is off putting from the usual Shantae charm. Thankfully the game still has plenty to offer in terms of DLC and extra modes on top of the base game, and is easily one of the best looking Shantae games out there.