love longplays, like you I see them like movies. Its not true that they lack narrative, some people actually take the extra step to provide comments while they play. For example the "lets play..." line of movies on Youtube tend to have them. Some (or should I say, most...) of them suck, some of them are pretty good at it
If you ever do a longplay, you'd be best to have a lure. For example a longplay that shows secrets in stead of just running through the game is worth watching. Let it contain something that gives people a reason to watch it in stead of playing through the game themselves again.
I'd focus on comparisons between different versions, now that would be useful
Nah, then Laffer wouldn't have anything to do anymore