I'm finding the new UI changes to the "Install plugins" to be less usable than previous versions. The double-line list item UI appears to be moving toward an iTunes app store look and feel. This is not a good thing. I see about half as many plugins which means more scrolling. The bundled plugins no longer have a heading for sorting. Perhaps the heading has been gone on the bundled plugins view for quite some time and I haven't noticed. This is more critical for finding plugins on the "Browse repositories..." dialog. With the changes I can only search, filter by category, and sort by name. Separate colums for category, age, downloads, and ratings allow for sorting by each attribute. This makes the plugin UI more difficult to use for discoverability.
Perhaps rather than reorganize the UI some cleaning or automatic filtering needs to be applied to the available plugins. Those plugins that are not compatible with the current version should be hidden or even removed. If there are any that are abandoned or no longer supported maybe those should be removed or placed in an "archived plugins repository."
I would like to see more of a "shopping cart" model for installing plugins -- add plugins to a "cart" and when finished "shopping" they are downloaded and installed as a group instead of individually. For example I've had problems in the past when installing the Scala and Play plugins together. Play depends on Scala but they don't recognize when they are being installed together; only if they're already installed and active. Play says that it depends on Scala and prompts to install again even though Scala was downloaded and installed but not currently active because the restart has not taken place yet. I would like to see engineering efforts applied to eliminating the restart IDEA requirement to activate new plugins rather than "improving the UI." To me the "Install Plugin" button in the right-hand pane adds a 3rd way to install plugins and serves only to make it seem more like iTunes.