Depends on how you want to construct the whole sentence but the nuance of understanding "life as ephemeral and ever-changing nature of beauty" should be expressed. This is not to express sadness as much as to show a resolution and acceptance life is indeed very short.

--- The "もの" in the phrase もののあわれ needs to be translated.
--- I am translating it as "The pathos of things."
--- Actually, this translation is taken from my dictionary which, I feel, express it poetically and very well.


You cannot appreciate this poem unless you are sensitive to the pathos of things.
ものの哀れを感じる人でなくてはこの詩は理解できない。(Source: Shogakukan Japanese to English Dictionary)

Also, I used "ephemeral" for 儚さ as it is also something that is not permanent.


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Note added at 7 hrs (2010-10-01 12:04:24 GMT)
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--- Just a thought.....
--- I personally like using the "The pathos of things" since it's the closest to the original Japanese, but the part "the ephemeral nature of beauty" (うつろいゆく美の儚さ) can alternatively be translated as "the fleeting nature of beauty".
--- They both mean the same thing, and it's a matter of preference, but I find them both to be poetic.