Slick.

That’s a fitting single word descriptor for 4 point Oh.

Some of the highlights:

• a scrollable grid of images and document thumbnails in the Media section
• editing area that fits your viewable screen area and scrolls with you
• easier visual / search / installation features in the plugin directory
• lots of performance enhancements and bug fixes

The overall look & feel in the Dashboard is a bit more streamlined and clean-looking as well.

As with most major steps in software release, there are a few discrepancies between WordPress and the thousands of plugins & themes developers have released to work with WordPress, but for the most part, this was a rather painless update/upgrade, all things considered.