I actually can respect AVGN for being able to go into some pretty big detail and history. Zero Punctuation doesn't do that...
I admit, at first I thought he was annoying after watching one of his more over the top videos. But then I saw his early videos and learned to appreciate them. What I like the best about his videos is NOT the swearing, the cheesy acting or the constant shock humor, but rather how he shows us WHY the game sucks ass.
Instead of just going "OMG THIS GAME BITEZ!!!!111111" he edits down the incriminating game footage. He shows us why the controls suck, why its so buggy and why the makers should be ashamed of getting away with releasing such an awful game.
And like you said, he knows his stuff. I really like how before he gets into the bashing he goes into the game's history. When it was released, why it was released, how people accepted it back then etc. It makes the videos far more fascinating that way.
Not to mention that James Rolfe, the nerd himself, is very passionate about his work. He loves making movies and you can tell he has a blast making the angry nerd videos. Recently, he did various reviews of the Rocky movie series and they were great. Hell, it got me to rent the first Rocky movie!
He also has a new short film called "Rocky jumped a park bench" which discusses the various landmarks seen throughout the movies.
Finally, James greatly appreciates his fanbase. I've seen him use a lot of cover videos of the theme song as well as artwork. That's something you don't see every day with internet celebrities. Yahtzee on the other hand, pretty much told everyone to "f*ck off" and don't bother him with review requests. While its understandable that he is busy and can't review every game out there he shouldn't have blown the audience that made him famous in the first place...
So yeah, the angry nerd videos are very enjoyable because the guy behind the camera loves what he does, knows a lot about the history of the games he reviews, respects the community that supports him and is very creative.