That is a simple question, without a very simple answer. I presume that you have read papers a selection of papers that have been published in Phys. Rev. Lett.?
I would aim to achieve similar or higher levels of excellence in:
a) The clarity of the written text
b) The significance (difficult to measure) of the presented work
c) The rigor with which the experiment was conducted and its data examined
Lucid, intriguing, and the caution and care with which the data are presented make this, in my limited opinion, a 'good' paper.
But the same can be said for a great many journals - what you may have to study is the particular 'style' or 'stance' of a journal - in the case of Phys. Rev. Lett. it appears to focus on fundamental, rather than 'fashionable', studies. And I applaud this.