How far can you stretch the excuse that a game is designed for children? At a rating of E10+, Shrek The Third is just too simplistic. If a ten-year-old can handle Super Mario, surely they will be bored with the single button attack combos necessary to take on almost any foe.
The gameplay is braindead and repetitive: run up to bad guys hit them until they die. Sure, you can do a few special moves, or if you want to make things really easy do a powered up attack, but there is nearly no need to. Occasionally you have to do a jump attack (gasp!) or navigate a 15 second "puzzle." A boss encounter with a huge ice dragon can be overcome by picking your favorite attack button and mashing it because you'll win in a brawl.
The only breaks from the liberal ogre smashing you dish out come from Shrek's pal Donkey giving a little lip and a handful of minigames. Though both are short, they give the game some of the flavor and humor of the movies. During a catapult game you have to aim your choice of siege weapon at the towers and fire by holding down a button for the correct amount of time. Hitting special targets unlocks special ammunition (eg: cows or big spikey balls). Sure it's been done before, and it probably doesn't justify buying the whole game on its own, but they're a nice break from the monotonous bad guy bashing.
Although There are a few chuckles involving Donkey, and using Puss-in-boots' special "cute eyes" move to daze foes is good for a smile, the majority of attempts at humor are tired and lazy. Most of the laughs consist almost entirely of fairy-tale characters talking with "unlikely" voices: valley-girls or surfer dudes.