D&D Basic Rules, and so far they've left me pretty unimpressed.
They're quite incomplete at the moment. Mike Mearls said that they would be "the equivalent of the D&D Rules Cyclopaedia", and maybe one day they will be, but right now they're not even close. They include no monsters at all, and they do include a huge amount of pointless fluff and padding — at the moment it comes in at just over 100 pages, and it could very easily have been edited down to less than half that.
That's not what's left me unexcited though. From what I've seen of them so far, they're pretty much just Pathfinder-Lite. They're a definite improvement on 4th Edition, but that was a pretty low bar. They're not a terrible set of roleplaying rules, they're just not very interesting.
Regardless of my own lack of enthusiasm for it, I really do hope that D&D 5th Edition is a huge success, because if it is it will bring more people into the hobby. I don't much care what they play as long as there are lots of them, because the spillover effects of a large and thriving market can be very useful in feeding the niche product makers who might be more likely to produce something I'll want.