I think the question of "what's wrong with rock music of today?" could be split up into two categories.
If you're asking about just plain rock music. Then yes it hasn't progressed as much as you might have thought.
If you're asking about heavy metal, for sure it's alive and well and probably just as popular the world over as it's ever been.
Being a guitarist/musician(started playing at 15, now 33) I'd have to say that "rock" has stagnated and as for quite sometime. However, "Metal" has gone through numerous changes and has many many sub-genres now.
You only have to look overseas to see the wide array of heavy metal and it's sub-genres. Power Metal, Black Metal, Melodic Death Metal, Epic Metal, Metalcore, etc, etc. Have all split or fractured from what we know as traditional metal.
The reason why Rock Music has stagnated is because of the blurring of the lines as to what is rock and what isn't. With so much cross-over stuff on the radio it's hard to decide what's rock and what isn't.
But make no mistake of that for Heavy Metal. Metal will never get the airplay it deserves and probably because most people in this country will never fathom the countless genres that exist in metal. For sure there are some bands that touch on the heavy side(5 Finger Death Punch, Avenged Sevenfold, Slipknot) but they're not that heavy. They would be classified as the heaviest of what the "radio friendly" metal has to offer but no where in the same class as most European Metal acts.
Rock has become more and more listener friendly(which is a good thing). Bands like Van Halen, Nickelback, Bon Jovi, Tool are all what I'd consider just regular rock music. It's not too heavy and lacks the uber deep and darker side of lyrics.
Gone are the days of where musicians in Rock and Metal(in the mainstream) actually applied themselves too their instruments. I became aware of music at an early age and remember most of the 80's rock and metal. Back then, guitarist actually practiced and tried to become proficient at what they did. Vocalist had exceptional octave ranges. Bassist and drummers were were sought after for their ability to follow the guitarist and be as technical.
While being an immense fan of Yngwie Malmsteen, Steve Vai and Joe Satriani. I also realize that those guys are already in the twilight on their careers. Gone are the days of the 80's when every new album they'd release was highly sought after by guitarist everywhere eager to learn the latest chops and licks from their favorite guitar gods.
If you look at the guitarist now in the more European metal acts. They've all taken it too another level good or bad. But the days of a guitarist being the dominant force that they were are gone and won't return.
I could go on and on for hours as to why rock and metal aren't the presence they once were but that would be too much.
But check out bands like Kamelot, Hammerfall, Primal Fear, Stratovarius, Nightwish, Iced Earth etc, that would be linked to the Power metal scene and you'll see it's alive and well. Just not here in America.
^^^^^^because Elize Ryd is so freaking hot!!
Here's a sample of Black Metal
Melodic Death Metal