The lameness of the prophecy was actually pretty awesome to me. Voldemort wanted it, but didn't know what was in it. Because he was devoting time to getting it, he wasn't spending as much time trying to figure out ways to mass murder, or even get to Harry as directly. The fact that it was, in the end, something Dumbledore already knew about? Is lovely to me. Its seems almost strategic to let Voldemort go after it like he did, because it might have been buying them time. And it also makes the final bit of Sirius dying seem even more tragic. The final battle was all about futility, and the fact that Harry's heroics aren't always going to work...so that fact that it was sort of a battle for nothing just makes it hit even harder.