Other vendors offer here a lot more settings and functions such as the Fritz box of AVM.
The firmware (as of January 2013) (@ Edit also 22/05/2013) is immature and full of errors. Device name, for example, often associated with the wrong MAC address. The web interface has to be started once again more often because the page depends.
There are 6 guest accounts. The feature is useful according to the description. Real gets but every guest access to everything. Neither IP addresses, nor MAC addresses or ports are filtered.
From my perspective, it's a big security hole in the Asus RT-AC66U.
Wireless Router without DHCP I feel like a car without brakes. The support is unhelpful. The only statements that one gets is that it does not go. It's like as if you complain about faulty brakes on BMW and get the answer "brakes do not go in this car."
I rather have the feeling to be a beta tester to bought as an ASUS product.
Obviously, now is also the ASUS way to leave the products ripen at the customer. One can only hope that it has matured before it was written down, because a newer product claimed the engineers.
Actually, I was always satisfied with products from Asus. Just as the firmware is now, I can only advise against the purchase but. Maybe it looks in 6 months from already different.
I still give it two stars because some works already.
@ Edit 22/05/2013:
The old mistakes and vulnerabilities were still not eliminated. Last updated ago already 2 months. Probably working Entwicker already on the successor. So I wonder if this device will ever be completed. Beaduerlich because the hardware is clearly better than the competition.