I would say you need a somewhat cleaner approach to placing things on the page. For instance, two paragraph breaks in a row are very non-idiomatic: try \vspace{2\baselineskip} instead. Instead of manually putting a hard space after punctuation, you probably want \frenchspacing. Also, using \sloppy as the default option is terrible. The purpose of \sloppy is to save a really bad paragraph that cannot be rewritten.

Visually, I agree that it is way too compressed, especially for a CV where the highlights should jump out at the reader. I understand you're trying to cram it into as few pages as possible, but you end up with horribly long lines. It could also use some vertical whitespace. If you must decrease the number of pages, think about trimming the content.

Just my 2 cents, of course.

What about the use of microtypography?

I think that you'd get optically cleaner margins (on the right) by using the microtype package. \usepackage{microtype} just works, though you could feed it \usepackage[expansion,protrusion]{microtype}. Since you have the \ifxetex switch and since XeTeX doesn't support expansion yet, you'd have to throw a \usepackage[protrusion]{microtype} in there, given that you have the XeTeX-microtype-package installed.

Why do you put a summary on your résumé as opposed to having it in a separate cover letter?

Have you gotten better responses after putting that summary there?

I ask because I've never seen it done and my first impression was to not want to read the résumé because of the wall of text. (I wasn't trying to hire you so my first reaction is probably biased, though)