Or not? Just curious 'cause this is a hot topic. Personally I'd say "not really", but they're an important stepping stone in the development of what we know as metal today.
It was categorized as 'metal' back in the heyday of the 70s, when the usage of electric guitars and vocal chords were not as brutal as they are today. The band, 'The The' was punk rock, listen to one of their songs now and it sounds like alternative music. Like you, I'd say they're metal, because they are the founding father of the genre.
I agree that they are. They're not heavy like, say, Motorhead. But metal comes in all shapes and sizes and Sabbath fits in without question.
Sabbath is definitely metal - their self-titled basically set up the mold for any doom metal band evar.
Definitely. They helped invent it, why shouldn't they be?
Well Metal is constantly evolving, and they definitely don't sound like modern metal bands such as Mastodon or Killswitch Engage. But you can't deny that they're pretty much symbolic of the Heavy Metal genre, which is where all the modern metal we know today spawned from.