First of all, I'd like to recommend the entire Scott Pilgrim saga. But I chose to only review this volume in particular because, in my opinion, it is the best one in the series. It may not be as charming as the first volume but it is the one that takes Scott on an emotional trip just as much as a physical one. What I mean to say is that the book puts Scott in tons of peril not only because of the 4th evil exe he has to fight but also because of his inner flaws and shaky past coming back to trouble him. In the end he grows as a character and so does Ramona, and everything turns out honky dory despite all their troubles and flaws. For me, this is O'Malley's biggest step in his saga and he does it exceptionally well. There are more reasons to enjoy this volume, but that's for you to figure out.
IN SHORT: IT'S THE BEST IN THE SERIES BECAUSE IT IS BOTH EPIC AND AMBITIOUS IN IT'S NARRATIVE BUT WHAT MAKES IT THE BEST IS THAT O'MALLEY PULLS IT ALL OFF VERY WELL.