Jeff spends most of his time filling Casey in on the lore of Guild Wars 2, detailing the story that leads to the alliance between the Humans and the Charr and the addition of the other three races of the game. He also discusses how the choices players make will influence their story experience.
Colin, on the other hand, is more focused on the gameplay end of things. He talks about how the game's classes will function without the omnipresent holy trinity, explaining that classes can fill various roles, which can be swapped between in combat. Dungeons are another topic covered, and Colin explains the differences between the story mode dungeons (which are more casual, story-driven experiences) and the exploration mode dungeons (which are tailored for more hardcore players seeking a challenge.)
For the full, info-packed video (plus an inside look at the swanky ArenaNet offices), click on past the cut!