I'll go ahead an promote this game a bit.
For 30$ (apparently not to everybody) it is a fantastic little puzzle game. Your challenge will partially come from the game, but will mostly come from you. You can't simply just throw something out to solve a puzzle and move on, and expect it to be a satisfying puzzle game. In older Scribblenauts games, you are required to solve every puzzle in different ways to get 100% completion. I think in Unlimited, it's just expected that you be creative and have fun with it. It's a bit like the Garry's Mod of puzzle games. Not only can you make anything (kind of), you can edit objects to create completely different things. Yeah, you can make an ultimate flying T-Rex with a wooden platform stapled to its back to do anything for you, but what fun is that compared to a helicopter tied to another helicopter with, say, a plank of wood precariously balanced between them?
If you aren't creative, the game's not worth 10$. If you are creative and can make your own fun, throw 30$ at it and enjoy. But, I really feel that the game needs a gigantic shining neon disclaimer of: You will hate this game if you want an enforced challenge.