So, for those of us who live under a rock, and for example, aren't subscribed or have only heard of him offhand, what exactly is he? What is his appeal? Is it like PewDiePie but less insane, is it more like ProtonJon but more technical, is it like TotalBiscut but less brimstone and hellfire?

All you need to know about JonTron.

Alright. Well spoken, researched, the sort of fellow who appears on camera but isn't a total git about it, a bit loud, not too energetic, etc...

The closest I can think of for PC are Lazy Game Reviews and Zero Punctuation.
LGR reviews classic PC games. Mostly in an informative capacity bit with sprinkles of humour. Zero Punctuation is made by a guy called Yahtzee Crowshaw. He reviews both PC and console games. He mostly reviews new games but has a long history with classic PC games. His stuff is mostly humour, he trashes every game. Even the ones he likes.
There's also Gggmanlives who sticks to FPS games, good and bad, old and new.

But if you want you want someone who just reviews bad PC games I'm afraid I'm not aware of anyone like that.

Honestly, probably LazyGameReviews.

http://www.youtube.com/user/phreakindee‎

And I wouldn't recommend Zero Punctuation to anyone. Not anymore, at least.

Why so?

He's not the kind of reviewer that acknowledges the good in the games. He spends more time grilling into their faults than anything else.

If I'm gonna watch someone review a game I'm gonna try to find someone who'll at least attempt to be objective about it... not litter his reviews with sex and poop jokes.

The sex and poop jokes I'll give you, it can get pointlessly gratuitous. As for grilling into the faults of the games I look at it like this. He's not trying to be fair, like I said even when reviewing his favourite games he totally trashes them. I'd never use Zero Punctuation as a buyers guide but it makes great comedy for games I haven't played yet.

I'm not really familiar with any of those Youtube reviewers as I'd rather watch some decent standup comedy but there's one classic video I remember that is quite hilarious, Spoony's review of Ultima 8 Pagan:

http://www.youtube.com/watch?v=wpui9EKNTzE

It's particularly funny for anyone who has played the game, especially before it was patched.
I love the game and feel very nostalgic about it but must admit everything Spoony says is technically true, unfortunately.

If it makes you feel better he did say in his interview with Richard Garriot that he does like Pagan despite it's flaws.

Like every one else here own all the Ultima games but I've played number one. I enjoy it but I keep on forgetting to take notes and forget what I'm supposed to be doing XD

Thanks guys. I already watch LazyGameReviews and I like his videos.

I'm a huge fan of TotalBiscuit myself, really good, honest first-impressions

Ancient DOS games: http://www.pixelships.com/adg/index.html / https://www.youtube.com/channel/UCUxuCVwzAsu41TI7UjOJYTA
LGR: https://www.youtube.com/user/phreakindee
PushingUpRoses: https://www.youtube.com/channel/UCCTNXqhWPba9Xh8gx0EKOtQ
TotalBiscuit: https://www.youtube.com/channel/UCy1Ms_5qBTawC-k7PVjHXKQ

Can't really think of any others right now that look at PC games.