Scribblenauts is a sidescrolling puzzle-esque game, you take control of a guy called Maxwell, and you are put in a small area where you have anobjective to accomplish. For example, get an apple out of an apple tree. You can then type out the name of any item (that is not incredibly obscure and isn't copyrighted) and it will appear in game (and has functionality similar to the actual object, for instance, you can summon a tank that you can drive around and shoot stuff with), you can then use that item to solve the puzzle (like summon an axe to chop the tree down and take the apple). Of course, there will always be multiple ways to complete the objective (instead of an axe, just give yourself a jetpack and fly up to the apple and grab it).
Scribblenauts has around 100 short levels, plus a custom level creator.
In addition to solving the game's puzzle's, I find it fun just to pit things against each other (god vs. cthulu, death vs god, kraken vs. the leviathan etc.)
Everything! and I mean everything not copyrighted is in this game (even some internet meme's) I'll give a list of some of them (and this is just off the top of my head):
God
Cthulu
Shotgun
Sniper Rifle
Leviathan
Ninja
Pirate
Atomic bomb
Large hadron Collider (it creates a black hole

Black hole
Nothing
Everything
Teleporter
Blaster
Lasersword (a lightsaber)
Excalibur
Rapier
Sword
Claymore (both weapon and bomb)
Dragon
Mind Control Device
Alien
Zombie
FTW
...
and it goes on... and on...
There are over 20,000 items in the game in total
Now if you see it in gamestop (or any store really) and have some spare cash to spend, buy it!
Some Links:
http://en.wikipedia.org/wiki/Scribblenauts
http://ds.ign.com/articles/102/1024059p1.html
http://www.youtube.com/watch?v=j3HXgvl8lp0