From what I've seen the Defender adds a massive amount of bulk. Some people may prefer that but some people wouldn't, and saying its not bulky is a little misleading. It may not be bulky to some but to most it is, especially for an already large phone. It adds close to half an inch to the thickness of the phone.
You can check out both the Otterbox Commuter and Defender cases in this video and see exactly how much bulk to expect when using this case as it compares measurements between the naked phone and the commuter and defender cases.