This looks like a very nice release. The OS exception hierarchy rework alone is worth waiting for, but the importlib improvements, the improved string representation, subdelegator generation, and the neater handling of chained exceptions are all things that people have been crying out for for quite some time. The *at() support (os functions taking file descriptors) is sure to be useful as well.
(But OS/2 support is dropped! How shall we survive in this harsh, cruel, Darwinian new world?)