There are $60 shooters out there with a main game that only lasts that long. . . I figure for an expansion 8 hours is pretty good. On the night Halo 3 released, I checked a few of my friends' xbl achievements and it seemed that they were able to make it through most of the single player campaign in only 8 hours. Most of them have the campaign completion achievement dated 9/25.
I'm playing through HL2 again before moving on to the episodes, and really enjoying it. The gameplay is good enough that it holds up against repeated playthroughs, and they have some really humorous achievements to track down.
