Any halfway decent band doesn't give a fook about tying themselves to any particular genre. NMA have dipped in and out of any style of sound if it was to the benefit of a song in question... and all for the better. I mean, can you imagine if they'd decided that the Vengeance / No Rest For The Wicked era was what they were sticking with and were still replicating those early tunes in the 21st Century? How utterly shite would those albums be (although, I suspect, that there would be a certain level of the fanbase who would love such a thing...)
Sometimes it doesn't work. Let me refer you to my very fave Metal band ever, Paradise Lost. Love this band... they started out as full on doomy sludgy rock with Cookie Monster vocals, started doing more melodic (but still very heavy) stuff, then had a couple of pretty successful albums with Icon and Draconian Times, cleaner vocals, catchy choruses but still fine and heavy musicianship. People forget that they were once tipped to be massive on the Metal scene, like playing arenas and stuff...
... and then they decided that they'd bring on the electronic side of things, make an album called One Second that was somewhat keyboard-y and then a follow up that sounded exactly like Depeche Mode. Don't get me wrong, I'm a huge fan of DM, I was all over that album... but it
killed them for a while, commercially and critically a huge failure! They made a succession of records that gradually brought back the heaviness (including last years Ascension which is one of their finest albums ever) but they're no denying that changing their style stuck a stick in their spokes.
Should bands amend or flat out change their style? I would say so... if they've got the nerve.
(oh, and it's not just two people... Shush pops in here occasionally...
)
