It's hard to say; so many great artists started with brilliant careers only to have their later work be "eh..." I understand that they need to evolve as artists but sometimes they end up alienating their audiences. Examples:
Red Hot Chili Peppers - I loved everything they did until after "Blood Sugar Sex Magik." After that album was "One Hot Minute" with Dave Navarro. I like Navarro's playing but not with RHCP and the only song I really liked on that album was "Aeroplane." Then, Fruciante rejoined the band and I was excited to hear what they would do; Californication was the answer and it is nothing like their earlier work. Everything I've heard on that album and going forward sounds mopey and depressing - much unlike the band that had written songs like "Mommy Where's Daddy," "Sex Rap," "Funky Crime," "Subway to Venus," and "Sir Psycho Sexy." Okay, RHCP has done VERY well for themselves and are probably more popular today than they ever were, but I don't like the direction they've gone in at all. I'm *still* angry about it.
Stone Temple Pilots - The first three CDs are great but the last one was not very good at all, IMO.
Guns 'N' Roses - Do I need to explain this one?
Back to your original question about Cobain, he might still be raging to this day and writing great music but, as often happens with angry young musicians, they become rich, comfortable musicians and it's hard to sing the blues when you own a mansion and a fleet of exotic cars.
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Devil's Advocate.·´¯`·..·»
"Nevver: Like the thing that hides in your closet. But worse." - Gueve
