Agreed. That's where metal review sites and blogs come in, and I just happen to help run one: http://www.metal-fi.com/ There are certainly loads of metal focused review sites out there, as well as nearly exhaustive encyclopedias like Metal Archives. What I felt was lacking was no one was really commenting on current production standards, or if they were, everything was "10/10 sounds great!" Bullshit. Nobody was regularly reviewing metal on vinyl either, and if you want something done right...
 

There is also the aspect that nowadays, most reviews of music/movies/books are 5 out of 5 stars.  If someone does not like something, they ignore it, rather than writing about it.

Actually that ties into the reason for this site, except in terms of music rather than headphones...

Hey, Dave...got any personal recommendations for an Opeth fanboy? Also a big fan of In Flames pre-RtR (some of their newer stuff is OK).

I'm generally pretty content with melodic, progressive metal, but Opeth is one of the few bands that takes me from chub to...well, the next level. Also found I like Steven Wilson's work as well.

To address the question raised by the OP...

I tend to think that mainstream music is not the place to look for when searching for high quality or innovative music.
Most mainstream music has always been the resort of the majority of the public and the majority is not very critical with music (for any number of reasons, but most probably simply because most people have other things to do instead of giving some considerable time to grow a true apprecciation of music) so pretty much any crap can sell as long as it's acessible or easy or makes people feel happy.
With time the discographic industry starts to see a pattern in the consumer listening habits and will try to export as much products based on the best formula to satisfy those habits, competition in this aspect is intense and as result the mainstream music landscape tend to be saturated with a lot of copycats and very few trully original artists.
In this circle the imperatives are to sell and profit, musical ambition or merit is not among the main concerns because the public does not demand such.
Musicians are either victims or accomplices of this industry.

There's a lot of quality music nowadays but there's a much higher probability of finding it by looking at a diferent circles instead of mainstream. As someone said before, it's a matter of looking in the right places.

Innovative music, though, is something relatively rare and much harder to find.
True innovation (either technical or linguistic) by nature never thrives from the mainstream, it's something that comes from the outer circles.
It comes from the "outside".
And it's something that generally is more frequent in the earlier stages of development of a discipline or art form and also tends to follow a shift or breakthrough in philosophycal, technological or social paradigma within a society or on a global scale.
It can also thrive from the pure "genius" of an artist, in which case, and just like with any other art form, it tends to be rejected or neglected by the mainstream audiences when it first makes an appearance, it takes time to fully be understood and accepted.

Music, just like any other art form, is very much an expression of the world the artist lives in.