It really doesn't matter if he is a "game reviewer" or not. He took money to say "This is a good product" in the U.S. we have advertising laws that say any advertisement needs to be made obvious that they are looking to sell something. PewdiePie's case is especially nefarious because his appeal is almost strictly small children. He could endorse skim milk and there'd be a small surge in skim milk as kids beg their parents for it. Celebrity worship is so scary particularly if it's affecting young kids who's brain haven't fully developed.

So we have a guy taking money to purposefully say "This is really good!". A small description is placed on youtubes native description box which is not visible while linking to just the video through PewDiePie's various other social media platforming. All is well? Nope. It's a video. If you were being an honest advertiser according to the FTC there would be a visual/verbal disclaimer clearly labelled in the moving picture screen box and not the word box. You can't advertise to people without telling them you're trying to sell them something.

If PewDiePie wanted to remain an autonomous let's player then he can't take money beyond his own revenue stream owed to him. The minute you begin taking money to endorse products you become a label, not a person.