Utopia is a great story with a mostly interesting and engaging plot, lots of cool concepts that are very well executed, and plently of good characters. It ties togethers bits from throught series 3 (and even the entire RTD era so far) to create a satisfying start to the series finale. The twist still makes me excited and I know what's coming - I can't imagine how exciting it must have been to watch as a Classic Doctor Who fan uppon release!