I have used Otter Box cases for the iPhone 3GS, iPhone 4S, and now the iPhone 5. The iPhone 3GS case was pretty nice, but the 4S case left a lot to be desired. By far, the iPhone 5 Defender Series case is a huge improvement over that for the 4S and is Otter Box's best iPhone case yet.
When Otter Box said the new iPhone 5 Defender case had a tougher rubber shell, they weren't kidding. The outer rubber shell fits securely around the case, even after a couple weeks of use and a couple drops. I bought my phone and case on launch day, and the case still feels like new two weeks later--no loss of shape, etc. The port covers fit securely, which is a big improvement over the iPhone 4S Defender Series case.
There's not too much else to say. I would definitely recommend this case to anyone who wants the maximum amount of protection for their iPhone 5. This case has definitely surpassed my expectations.