Above you can see a YouTube video “found by MacRumors and posted by f1ipzid3” that shows a side-by-side comparison between the iPhone 5 and iPhone 4S video taking abilities.

Comparing the video shots from the iPhone 5 vs. iPhone 4s
This video looks at indoor and outdoor light, front and rear camera, depth of field & also notice the difference in stabilization.

Both iPhones were handheld on top of one another to have equal comparison
All Video has not been altered other than cropping/sizing