This isn't very known. The talk pages of the most controversial Wikipedia articles usually have a wealth of additional information that hasn't yet made it to the main article [and some of it will likely never make it]. Types of information in talk pages includes facts for community consideration, opinions, concerns, claims, rants, unproven "facts", food for thought, requests for edits, and so on. If you're looking for a comprehensive, holistic picture on something, then you should definitely look at the talk page of an article.
For example, the article on the controversial Gaza flotilla massacre incident includes a lot of information in the main article body. However, if you visit the current talk page or any of the several archived versions [1, 2, 3, etc.], you'll realize that there's a wealth of additional information out there in these pages, and reading it can add much value to your overall impression.