Alternative Rock had an immense level of variety in the early to mid 90s. There were a ton of stinkers, but not nearly as many as there are now. I think mainstream music as a whole has become tearfilled baby gibbering or the equivalent of nursery melodies given heavy/badass tones/beats. Agree or disagree, I think alt rock served its purpose but no one's really stepped up and made it cool again. The Mars Volta are doing a bang-up job, but they're really just laying the experimental groundwork for the next wave of "rock." Whether we call it rock or not doesn't matter, I don't see the elements of the genre dying out. Maybe the drum, bass, and guitar will slowly lose relevance to each other, but that doesn't mean the end of riffs or jams.