Then you're not listening to the right metal.
Some of it is ****e, but there's alot of good stuff there. System of a Down, Machine Head. These bands do a great mellow number too. Or Fear Factory - not everyone's favourite, but their singer has a very well trained voice - he can hold a tone for a bloody long time. Some of it is 'shouting', but that's the style. But this guy had to train his voice for a long time to do that well, or he'd have ended up with throat cancer.

You're probably judging your opinion on the crap bands...

And I'd call Zep 'rock'.