Having used the beta, and as a Scala developer on a large multi-module project, this release is a game-changer performance-wise. The memory footprint is a small fraction of what it once was (literally). While memory is not really a big issue for a developer these days, this is huge because previously we were forced to run at large heaps, which would cause 'fun' GC pauses while typing. The code completion is now fast enough to put back into auto mode. Similarly, the find functionality is now instantaneous, even when you're finding variables. They've clearly been playing around with threading on the editor, because there seem to be many fewer situations where typing slows down while the system is thinking about other things.
I've appreciated every IntelliJ upgrade. IntelliJ was 'mature' many years ago, but they continue to push and push and rethink features and experiment. This release just wowed me enough to gush about it :).