This is a very well-executed theme. Coded with great attention to detail, with a beautiful clean design and nice typography. Good color scheme, lovely options page with support for a number of beautiful typefaces. The theme has a responsive design that works equally well on computer, tablet, and smartphone screens. Four out of five stars.
Due to the relatively transparent php, html and css code (inherited in part from the Hybrid core by Justin Tadlock), Oxygen is easy to customize. A child theme is created in seconds and a customized site can be up in a few hours. A great basis to work with as a parent theme, but perfectly ready straight out of the box as well.
Why not five out of five?
For two reasons:
1. The included page templates aren't flexible enough, which hopefully will be improved in future versions. The full-width template is truly full-width; it would be nice to have it optionally with a sidebar. The front-page template is gorgeous but a bit inflexible in terms of setting up: all front page posts have to be hand-picked using a custom post_location metabox and the featured content slider does not support sticky posts. Further, sidebars are handled in an unintuitive way, with the call for the secondary sidebar being buried in footer.php and the sidebar being disabled for the full-width template in an "offhand" way via functions.php. At these and other points, the code of the theme is less than transparent.
2. The theme is perhaps a bit too heavily based on Hybrid, with a lock-in effect. Although Hybrid is a great framework, its downside is that documentation is sparse and support forums are hidden behind a paywall. This makes it hard to find good supporting information for some of the core features of the theme . For instance, a lot of metadata is called using Hybrid shortcodes like [entry-author] etc. It is hard to find out how to work with these shortcodes (and especially how to customize or translate them) without paying for Hybrid, which is not at all clear when you first download Oxygen.