Although the adjective qualifies 'metafísica', I believe that in the case of this philosopher the idea of a total rejection of metaphysics is fundamental, and my answer ties in with the meaning of the rest of the sentence.

Nietsche's purpose was to break away from "traditional" metaphysics but some say he never managed it:

"Friedrich Nietzsche is generally received as a clever critic of metaphysics who nevertheless remained hopelessly entangled in the metaphysical tradition he sought to challenge."
http://findarticles.com/p/articles/mi_hb3545/is_n3_v46/ai_n2...

It is one of those sentences that need the full context next to it, otherwise it is difficult to know which is the 'right term'.

I suggest "proper" as another possibility, but it will depend on the rest of the article. "Genuine" could well work, but it has huge connotations which may be the author would prefer to avoid. The same applies to "authentic".

The advantatge of "proper" is that it does not have any apparent baggage.

My comments are based on years of experience working in the field of philosophy, both as an academic and as a translator.

I hope this helps.

Quim

My understanding