kain_kusanagi on 14 October 2012
Fair use allows for bits of copyright content to be used for the purpose of critique. All those "Let's Plays" aren't reviewing anything. It's no different than running a ripped movie on youtube.
If you want to do a legitimate review there is a legal way to do it. But if all you are doing is uploading long videos of games, movies, etc. then you are breaking the law.
