Yeah I'd agree about the songwriter part, I'm just so confused as to how he was able to even write songs (I know they're not technically complicated) without almost any knowledge of what he was really doing on the guitar. It's fascinating to me I guess, because I wouldn't have the confidence to do that not knowing more than most other people with guitars.
I just watched the nirvana DVD. It wasn't just him. The drums and bass add a huge element in each build up of every song. His progression and song writing approach wasn't difficult. If you follow the idea of how song writing works you'll get it..
1. The melody and how it progresses.. he did this with his clean chorus effect a LOT. Then he simply distorted it. Easy build up method.
2. Chord progressions. Many chords of his were the same chord progression. But you'd never realise it unless you listened to the songs after another. But simple pop chord progressions.
3. He had fun with it and didn't care. You could tell he out his solo Into it. In part to his vocals..he had crohns disease so that definitely effected his singing ability. I think he enjoyed screaming more anyways.