"Rycon Roleplays" is pretty great. He makes Bethedsa games like Fallout 4 and Skyrim a lot more interesting than they actually are. I recommend his Fallout 4 Frost permadeath series as well as Skyrim: Tale of Leonidas... he has a lot of other content, including many non Bethesda titles, but I haven't had the time to watch it all.
"Tapcat" is a great channel for XCOM Enemy Within, XCOM 2, and other strategy titles like Civilization 5...
"Smudboy" does a lot of critical analysis of game franchises, mostly Bioware related stuff... don't even bother if you are a fanboy though lol. Although tbh it might open your eyes to the flaws of their games, so who knows...
"Tehsnakerer" and "nerdSlayer" have been mentioned already... I recommend both.
And I'm going to end this with "Larry Bundy Jr," who has some very interesting retro game related videos in his "Fact Hunt" series.
Edit: Actually, if you like Let's Plays, I'm going to go ahead and add "Zemalf" and "ChristopherOdd" to this list... like TapCat and Rycon, they are both... well, more professional and subdued than a lot of youtubers, but still entertaining and in many cases true masters of the games they tackle.