Part of The Orange Box review.
Taking off straight after the significant event that ends Episode One, this next instalment has a very different feel to it. Whereas Episode One was stuck in corridors and basements, Episode Two takes you out of City 17 altogether. It much more closely resembles the early chapters of Half-Life 2, where you get to roam in open, varied settings. Plus, you are once again provided with a vehicle to get you from one fight to the next.
I wasn't hugely impressed with Episode Two at first, because your first destination turns out to be a subterranean antlion colony. The colony section isn't bad, it's just limited to fairly tight-quarters dodge and kill. However, most of Episode Two takes place on the surface, on roads, in villages, and in lush green glades. The open areas allow for more freedom and tactial manoeuvering, making the game feel more interesting.
Half-Life 2: Episode Two introduces Achievements, which are goals that you can aim to complete purely for amusement. Unlocking an Achievement causes it to remain in your persistent stats on Steam, but it does nothing else for you. Some of the Achievements are impossible not to earn if you complete the game, being awarded simply for completing certain chapters. Other Achievements are so unlikely that I find it hard to believe more than one in a thousand players will unlock them, such as sending a garden gnome into space (which would require keeping the garden gnome with you through almost the entire game). When trying to view my Achievements, I frequently received a message along the lines of "You must be connected to Steam to view Achievements", which makes me wonder if half of the Achievements data gets lost. So not a hugely valuable addition to the game.
Something else that didn't impress me was a serious problem with some of the dialogue scenes. As the Vortigaunts began their ritual, my game suddenly started to stutter, and the sound vanished. The frame rate must have been down to about one frame every two seconds, and without subtitles turned on I'd have had no idea what was going on. This continued until the next LOADING message appeared, at which point the game returned to normal. The same problem ruined the end sequence for me too, which is a shame because it would otherwise have been quite a shocking end to the episode. Luckily this problem didn't affect any of the gameplay sections, but it's still quite disappointing. I'm not sure if this problem affects many other people.
Problems aside, Half-Life 2: Episode Two is an excellent addition to the series. The hunters make for a strong new enemy, and the end battle is great fun, the Magnusson Device being quite a challenging weapon. The extra story elements revealed in Episode Two make things more interesting, and I look forward to Episode Three, which may centre around an Aperture Science ship known as Borealis.
2008-11-30: I completed Episode Two again recently on my new gaming rig, and there were no problems at all during the dialogue scenes, so either an update from Valve fixed the problem, or it was something about my old machine that was causing the game to get upset.
2010-09-01: See my review of the Novint Falcon game controller. It adds quite a lot to the Half-Life 2 experience.