Alchestbreach is my personal favourite. Although, I'm sure that he isn't to everyone's taste and he doesn't focus on RPG games specifically. He cut his teeth on New Vegas and has literally hundreds (possibly thousands) of New Vegas videos. He now does Fallout 4, New Vegas as well the occasional miscellaneous title.
Gopher is a solid choice. He is big into immersive, atmospheric games. I think right now he is in the middle of a Witcher 3 and Fallout 4 playthrough. He sets a very slow, methodical pace so you need to be a little bit patient or else you might get frustrated.
Someguy2000 is also very entertaining albeit pretty much unknown. He is a FNV and Skyrim quest mod author who started doing lets-plays. He has since dropped off the radar but he has done that before and always comes back. Fair warning, though, his videos are not for the faint of heart. He gives absolutely zero fucks about video editing, sound quality, etc. He basically just gets drunk, plays games and gets irate. Don't be put off though, he has a lot of interesting and hilarious things to say.
