I'll be honest, I went into it a little dubiously (I've bought things before that critics and other people have loved and hated them), and was more than a little uncertain about the first volume, but by the time Kim Pine gets the excellent line of 'Scott Pilgrim. Cue applause' in volume 2, I was hooked.
I just love how quirky it can be, and the little things like Scott always calls Stephen Stills Stephen Stills, whilst everyone else just calls him Stephen, but it was little things like that and the way O'Malley carefully revealed pieces of history that gave his characters so much depth in amongst the zaniness, and it just worked, for me.