Levels have a "par" associated with them, which is the number of objects the developers reckon you may need to use, and using fewer objects means bonuses, as does picking stylish options and completing the level quickly. Using an axe to cut down a tree is effective but obvious - why not use a sword instead? Or termites? The better your score for a level, the more "Ollars" you receive to spend on things in the shop - avatars and songs, in the build I have. You can also earn "merits" for things like not using guns. Plus there's a level editor, which offers you the existing layouts as a template and lets you insert your own objects using Writepad and then script behaviour for them (bear protects porridge, for example, or lion attacks crocodile) with a few taps of the stylus. Replay value is a potential concern, or at least it was until I replayed a level and discovered "Advanced" mode, where you have to complete the same task three times in a row without using any of the same objects on subsequent attempts.
The physics are a bit too rigid sometimes - it's nowhere near as much fun to beat a level by lucking through it thanks to a physics spasm, accidentally bouncing a girl into a pond with a wall, as it is to implement an elegant outcome, finding a way to divert her ascent up off the diving board deliberately. As the difficulty increases, 5th Cell also introduces more fiendish level designs. There's a Starite in an ice block suspended over lava, with an unavoidable trip-switch preventing you reaching it before it falls; later there's an underground level where you have to contend with big gaps as well as total darkness to lead a boy back to his father. You could do with more hints in these situations, and you might discover control quirks kill you off unexpectedly. For instance, instead of climbing a ladder and hopping onto the next platform, Maxwell sometimes falls into the pixel-wide gap between it and the ledge until you go back and forensically reposition it. It would also be nice to stop the camera resetting to Maxwell after a few seconds of inactivity - sometimes you just want to stare at a setup on the other side of the level and ponder it.
On the whole though the controls are intuitive and graceful, and levels are quick to reset if you want to try something else. It really shouldn't be taken for granted just how miraculous the Objectnaut system at the heart of Scribblenauts is, either, but the truth is that the reason the game works so well quickly blends into the background, and you never find yourself questioning it or wondering about anything other than what's in front of you. Where there's potential for confusion, the developer's rigorous playtesting has nixed most of it (and so you're offered multiple choices if your chosen word is ambiguous, or if you try to perform an action with an object that could be thrown, placed or whatever), and elsewhere the goodwill the game elicits within half an hour of your turning it on overrides any niggling concerns.
Typically if a creative-solution sort of puzzle game is going to go right, it's down to the clear definition of its rules and the developer's own creativity and intuition. Portal and World of Goo are very flexible, for example, but their success owes just as much to the skill with which Valve and 2DBoy wielded their respective concepts as it does to the Aperture Science Handheld Portal Device or smiley faces and blob physics. Having played through 40 of Scribblenauts' 220 levels, it's not quite accurate to say that it's an exception. Level design can afford to be rudimentary for a while, because in the absence of perceptible limitations your level of enjoyment is determined by how much you invest in it, and by sharing solutions with other players. But as the novelty wears off 5th Cell will need to answer with levels that up the ante without bamboozling you completely, and it won't be possible to tell whether it's done that until we see the other worlds in full, which we should do closer to the game's 25th September release. To say I'm looking forward to doing so, however, is an understatement.
Scribblenauts is due out exclusively for DS on 25th September.