Episode One is a satisfying combination of the familiar and the new. It's a constant rollercoaster of taxing but rewarding challenges, many of which intentionally subvert the expectations of anyone familiar with Half-Life's style of gameplay.
Any quibbles - we were always going to want it to be bigger - are minor. Indeed, the frustrating command system that gave orders to citizen squad-mates in Half-Life 2 has been replaced by better, more reliable AI. And Episode One's superior pacing, voice-acting and storyline make other games look stupid in comparison.
Half-Life 2: Episode One demonstrates how games ought to be made, forged by dedication, imagination and more than a little risk-taking. It's an outstanding, stirring experience. And, with two more episodes due between now and the end of 2007, things are only going to get better.