Thanks for the contributions folks, some really interesting points and links. I have to show you this though, I found it strange and funny:

https://youtu.be/MOOCV7sYFWQ?t=4m51s

How can you make that mistake?

1. They're usually annoying
2. They're usually boring
3. They usually try to hard to be funny which makes them not funny
4. They try to hard to be scared when playing horror games
Yeah there's more I never watch youtubers play games. I watch montages sometimes and reviews and Ruleof2review (he kinda just talks about games) but that's all.

Watching them is my way of finding out if the game is interesting enough for me to get, like how I watch review videos though I respect their opinion, I don't always agree with them.

2 things, when they title their video with "Walkthrough" but know nothing of the game or where to actually go etc., second, when they don't read tutorials/descriptions in the game and say "what the hell was that? why was it too strong? bla bla bla?" hehe though it's fun to see them suffer from their mistakes at times .

When they make excessive and unecessary sounds and effects to be more interesting

Walkthroughs that are disguised as let's plays. It's annoying when I'm looking up for a guide and the person playing is making a bunch of mistakes or has no idea what they're doing.