I'm glad you asked. It gives me a chance to bore more people on my own badly argued opinions.
I've been a metal fan since (roughly) the age of 11. I'm 30 now. I remember the big Thrash explosion back in the day, which was really "my era" the first time around. I have noticed that metal has gone through quite a few evolutionary steps since then.
Currently, metal stands in the balance. I prefer the current crop of bands more than say, a few years ago. I didn't like the "nu" metal and "rap" metal movements at all, but I do like quite a few of the newer bands (I like God Forbid, I quite like Trivium and Killswitch), but the cult of the "trend" is bigger than ever. THis whole nu-emo thing really pisses me off. I turn on the TV , and all I see are wave after wave of indistinguishable crap haired bastards ripping the accessible parts from metal, taking the piss out of it in their ironic t-shirted floppy haired way, and crooning over the top of it. Happily, I think that this current wave of crap is on its way out.
Of course, the problem is that with a wave of popularity in heavier music, you get the scene jumpers and the false-fans. I remember 1994-1997, which were terrible years for metal fans, and fans of underground / extreme metal in particular. I'm a big thrash/death/doom metal fan and a luke-warm black metal fan, and in 1996 or so, death metal was dead in the water (sic). A few of us hung in there, and now death metal is healthy again. I bought all the Anthrax albums in their "falling between record companies" years, and happily they are in rude health again.
My (long winded and drunken) point is that I think that the current good state of metal might be an illusion. What counts in the long term are the long term fans, and only time will tell if they stick with our music after the trend dies down again.