An interesting platformer, hard swings in difficulty
Giana Sisters' games have a sordid history. The first one wasn't so much a game as a complete rip of Nintendo's semi popular Super Mario Bros. with Mario & Luigi replaced with the titular Giana Sisters. However since then, the characters have come to star in their own series of original games including this latest one. You play as Giana trying to rescue her sister Maria from the dream world. The set up is really quite loose, but it basically boils down to a series of 2D platforming levels.
The interesting twist (ah) in the game is that Giana can alter the dreams based on which of her two powers she is using. Her fireball attack (kind of like Sonic's spin dash) makes the dream world dark, evil, and full of demons. Her cuter mid air spin, which allows her to descend slowly, makes the world into a happy fairy tale world where the enemies are owls. Switching back and forth between the two sounds dull, but it's actually some of the most interesting platform design I've played in a while. Other changes include red and yellow gems only able to be picked up by the version of you with the right color hair (fireball = red, cute twirler = yellow), certain platforms vanish if you're the wrong color, even some enemies have different properties in the two worlds.
The only major complaint I can level against the game is the difficulty. Boss battles seem unnecessarily difficult and frustrating and there are a few platforming challenges that seem ill-conceived. These gripes are few and far between and the game is a true gem and totally enjoyable. Give it a shot if you dig interesting platformers.