BIOS and Software
One of the things I've long praised ASUS for is the execution of their UEFI / graphical BIOS. Not only is navigation smooth and seamless, they never forced you to rely on the mouse, and the keyboard navigation worked just as it always did in legacy BIOS. Ontop of that, I think they did the best job creating a functional "simple BIOS" which allowed you to get right to the quick things you might look for out of frequent BIOS entries, like force booting from a particular device without manually altering boot orders or applying a quick automatic tune for more performance or efficiency. And, although it doesn't drastically change my experience (which was already entirely positive), ASUS has further cleaned up the GUI, further streamlined navigation, and added a few neat features like the ability to leave yourself notes from, say, an overclocking session, for future reference. Of course it includes the full range of tweaking options you'd expect from a capable overclocking board, but scaled back a bit from the Deluxe-level enthusiast boards.
AI Suite 3
This is going to sound like a broken record after reading about the BIOS, but AI Suite 2 has been a crown jewel for ASUS since they've rolled it out. The aim was to not only provide most of the BIOS-level functions on the desktop GUI (which can be more user-friendly and minimize reboot times), but to also cleanly and unobtrusively package all of the nifty features into one clean software package instead of installing a dozen tiny individual software packages which becomes unwieldy and outright annoyinig. AI Suite 2 was great, we've raved about it's ease of use and functionality before. Here's a detailed look we've written about before, and AI Suite 3 continues the same great experience. Access to overclocking features, system monitoring, and custom fan speed profiles, to name a few of the big hitters, still really enhances the overall experience in a big way. Overclocking is much less of a PITA without having to worry about constant reboots, and keeping your rig as quiet as you'd like based upon target temperatures is fantastic. Again, ASUS hasn't tried to fix something that isn't broken, and has instead further refined and streamlined one of their best experiencial features in class-leading fashion.