Insight includes Prior Knowledge/In-depth Knowledge that can be adequately conveyed.

[Opinion] http://www.youtube.com/user/Campster
Pretty much does High School Level Analysis in Game Theory .. The guy recently discovered his style of opinion.

[Insight] http://www.youtube.com/user/SirEldricIV
Doesn't really waste the viewer's time, and commonly explains game mechanics as far as how it works, and how to progress, with some personal involvement [fluff?] that isn't too irrelevant.

[Voice] [Humor] http://www.youtube.com/user/GrimithR
Look at his Fallout, and Master of Orion Series, if not, Spirit Engine 2

[Voice] [Insight] http://www.youtube.com/user/Adkit2
Avoid the Max Payne 3 playlist, that's more or less him playing for kicks, not recording.
This guy is a Swedish Chef, so enjoy that. He is also the HERO.

Other tips ..
Please don't try to voice act what people say, only few people can honestly do it.
Be articulate, please don't sneeze/cough/drink on mic.

etc etc