The demo (1 gig in size) is available as a free download on Xbox Live and it is worth snagging. Although only one-fifth of the mall is available in the demo, there is still much there for you to have fun with.
Beyond a doubt my favorite moment so far was running behind the counter in a cafeteria, picking up a frying pan and heating it up on the gas range. Then, as the zombies began to crawl their way over the counter to get at me, I turned and literally melted their faces off with the bottom of the red-hot frying pan. Not sure what was funnier: the charred dripping face or the "sssssss" sound that accompanied the attack. When the frying pan eventually cooled off, I used it to knock about 30 zombies unconscious before breaking open the display case of a jewelry store and throwing dozens of gems at the undead pursuers.
This is as freeform a game as can be. There are over 50,000 zombies in a gigantic mall and nearly everything you would expect to find in the mall can be used as a weapon. Good wholesome entertainment!