As in what? Not being "limited" to metal any more? Since when was metal a limited genre.
Since you said it should not include influences from other musicforms. Metal is a genre, all genres are categories and all categories are limited. If it was not limited they could include any music style they wish. And I think they should. As long as the result is good, that is.
If that's happening to you it just means you're not listening to a good metal band.
I'm not sure what you mean by this. Do you mean that bands cannot be good and include other forms of music at the same time, then ofcourse it's
your opinion. But if you mean that if a band, like Therion for instance exclude all non-metal elements from their music then there won't be much metal left to call the band a good METAL band, then I agree. However, that doesn't stop them from being a good band or fit in the genre.
If a band can write a good metal song then usually outside influences are either used sparingly (alongside the metal) or not at all.
I don't know. I mean, Hollenthon writes great metal songs, so does Rhapsody (if you are into powermetal) and Dimmu Borgir. Yet they also inlcude lots of elements of classical music.
I don't think metal bands (or any other bands for that matter) should write music based on genres. If a band likes 'pure' metal, and writes the best songs keeping within metal, then they should. There's no need to add classical elements just for the sake of adding classical music, like Metallica did with S&M. In that case I much prefer what Rage did with XIII, or what Dimmu Borgir has done with their latest release, used the non-metal parts to express their ideas.
Including a string/horn/acoustic/choir/rap/techno section to make up for your lack of riffs and songwriting is definatly not creative.
Ofcourse, so is using alot of riffing and solos to make up for bad song writing.
But ofcourse, that's a taste thing.