The R8500's feature set is very similar to the R8000's. We described common features pretty well there, so only differences will be covered here.
Basic mode status
The first big difference is the Dynamic QoS feature. Here's how NETGEAR describes the feature in the User Manual:
Dynamic Quality of Service (QoS) helps improve your routers Internet traffic management capabilities through better application and device identification, bandwidth allocation, and traffic prioritization techniques. Dynamic QoS resolves traffic congestion when the Internet bandwidth is limited and different demands compete for bandwidth.
You just enable the feature, manually enter your ISP up and download speeds or use the built-in Ookla speed test applet. Dynamic QoS uses a database to identify application signatures to better classify traffic. My first attempt at manually updating the database just hung. A second attempt reported "No new database version avalible".
Once enabled, you can see what Dynamic QoS is doing, but you have to manually refresh the screen. You don't get a breakdown of individual application priority, just the by-device view shown.
Dynamic QoS monitor
You can manually set device priority to High, Medium or Low, change its name and device type.
Dynamic QoS device edit
The Access Control feature lets you block devices entirely.
Features - Wireless
NETGEAR's Smart Connect implementation hasn't changed from the R8000's, remaining the most conservative. Devices are steered between the two 5 GHz radios only once when they connect and band-steering (between 2.4 and 5 GHz) is not done. The SSIDs and wireless passwords have been changed from the defaults in the screenshot below. NETGEAR assigns unique SSIDs to each router and radio and fairly strong wireless passwords, too.
R8500 5 GHz radio settings
Note Smart Connect is not enabled by default. When you do enable it, the second radio settings are greyed out and the 5 GHz-1 radio SSID is used. Because band-steering isn't done, you still get separate 2.4 and 5 GHz SSIDs when Smart Connect is enabled. Of course, if you want to roll the dice on how your devices connect, you can set the 2.4 GHz SSID to the same as the 5 GHz'.
5 GHz-1 is the high-performance 5 GHz radio because it's connected to the external amplified antennas. It defaults to Channel 44, but you can set it to 36, 40 or 48. The 5 GHz Mode controls settings are Up to 433 Mbps, Up to 1000 Mbps and Up to 2165 Mbps for 20, 40 or 80 MHz bandwidth modes. The 2.4 GHz radio Mode settings are Up to 54 Mbps, Up to 433 Mbps and Up to 1000 Mbps. The User Manual provides no guidance to translate these. But I'm guessing Up to 54 Mbps is for legacy device (b/g) support and the other two are for 20 and 40 MHz n/ac devices. 80 MHz bandwidth is not supported in 2.4 GHz.
Advanced Wireless settings are shown in the screenshot composite below. You see universal wireless bridging (no WDS required) is supported via the use other operation mode checkbox. Only one of the 5 GHz radios is used to bridge; whichever is needed to connect to the primary router's channel will be used.