Some of the more popular Let's Play video casters are:
Guy#1
Announces he's never played the game before, spends about three episodes fumbling with the interface and basic concepts of the game, and frequently states he's an idiot. It's great fun watching him constantly miss the point, begin sentences he's unable to complete, and switch focus to completely irrelevant junk to fill the gap. I usually thumbs-down that guy and leave immediately.
Guy#2
Announce he's played Version 1 of the game, and then spends the whole series explaining how in Version 1, you could do this-or-that. Apparently his audience does not contain people who played Version 1. It's a drag listening to him drone on about his memories of a game he's not playing, like listening to someone narrate their vacation videos.
Guy#3
Spends the whole episode talking about his Other let's play videos that you should check out, and his personal life, his cat, the reason he didn't post a video yesterday, why the sound quality sucks and the music is too loud, his new computer....Anything except the game.
Guy#4
The unpaid salesman/fanboy, spends most of his time awash in blissful praise of never-before-seen technological advancements such the high quality graphics of the sky box, how the development team actually went ahead and implemented shininess, the attention to detail of how there's a cow munching on grass in a field, or little guys walking around in a city. Amazing new developments that astonish and bewilder the childlike mind of someone who's actually seen all those features before in many games, and is totally lying about it.
Good Let's Play videocasters are hard to find.