With "Let's Plays", you're there for the commentary, it's not just a quiet walkthrough. The downside of this is that you, as a viewer, have no timely input (episodes are sometimes done in batches and uploaded over a week or two). But.. maybe that's the attraction, back to the days of yore when you would yell at the Jeopardy/Wheel of Fortune contestants for not getting the obvious answer!

Source: I watch LPs constantly while working, it's good background noise and gives me an easy outlet to divert my attention.