Chuck's Challenge is a game about a guy (Chuck) who's been kidnapped by a purple alien monkey-thing (Woop) and forced to create "games" for it to "play" because it's bored. I think. It's essentially a follow-up to Chip's Challenge, with the original game's creator, Chuck Sommerville, acting as both the designer and main character.
Niffler may have carried over a good deal of concepts from the older title, but the most significant aspect is the community integration. Sure, Chuck's Challenge features 100 levels, about a quarter of which are free (the rest can be bought through in-app purchases), but the real draw is the ability for users to create and share their own. In a way the concept's not all that dissimilar from Media Molecule and their community-centric platformer, LittleBigPlanet.
Level editors and sharing aren't new ideas, even on iOS, but they're very rarely incorporated as lovingly as they are with Chuck's Challenge. Heck, the entire game is essentially designed and built around the concept of creating and sharing levels among the community. I kind of wish more games, both on the App Store and just in general, would think about doing things like this more often.
Chuck's Challenge is available right now for absolutely nothing. Check it out, maybe?