Shantae and the Pirate's Curse was the first Shantae game I felt compelled to give a proper chance. I'd played the previous two games for a few minutes each, and while they were okay, they didn't keep my attention for long.
Ironically, it was taking away Shantae's genie powers that made Pirate's Curse click for me. Now just a regular human, Shantae needs to rely on pirate-themed swag to traverse the islands. They're rather unorthodox in their usage as well, like a pirate hat as a parachute, or a cannon that blasts downwards acting like a quadruple jump.
It means you don't ever have to stand still and dance to transform into an animal, which improves the pacing dramatically. Dancing didn't take long to do in the previous Shantae games, but over time it added up to too much watching Shantae wiggle her belly. In Pirate's Curse, Shantae just uses the items and that's it.
It does bring the Shantae series more in-line with regular Metroidvanias, but it's still a welcome change. Future games would strike a balance between quicker ability selection and the dancing that the fans liked from the previous games.
I'd actually say that Pirate's Curse is the best place to start with Shantae if you've ever had a passing interest. Its levels are well designed, the soundtrack has some absolute bangers, and the whole game still holds up well to this day.