I have a little different opinion on them.
I tend not to like the video LPs, mostly because I don't want to be talked at by someone who isn't much of a voice performer, and because they include all the less interesting bits of gameplay, whereas a screenshot based LP can skip around and just present the good bits.
Also, I find the best LP games tend to be of those games with either a high inherent variation, either through slightly randomized generation of content or through massive scale, because that means that the game experience that the person presenting the Let's Play shows in their game is not necessarily the same as the one I would have if I played the game myself. I tend to find that the best Let's Plays come from either turn based games, 4x/Management games, or grand strategy games. (Like X-Com games, shameless fucking plug [http://www.escapistmagazine.com/forums/read/362.82574?page=1], but also Hearts of Iron, Civ, Dwarf Fortress, etc can make good stories which aren't the stories that my game would have told)
A game with low inherent variation (most action games, heavily story driven RPGs, etc) don't significantly vary between plays, so a Let's Play of, say, a Final Fantasy game would be very similar to the game experience I would have had if I'd played it myself, which is not so interesting.