I've read XPS specs [1] and from the looks of it it's a very sane format, which I cannot say about other Microsoft XML formats I've seen (such as MS Word XML). I'm not that familiar with PDF internals, but I really doubt XPS has much inessential complexity. And, being a new format, it has zero legacy issues. The common complaint against PDF is that it's hard to extract text from it, but with XPS it seems to be rather easy and can be done with the standard XML toolchain. Besides, it has a good support for document structure: it has not only document outline, but also stories, sections, tables, lists, figures, etc.

http://www.ecma-international.org/publications/standards/Ecm...