No problems here with DIR-855 and latest firmware.
Wireless is stable (with 11N clients only). 5GHz radio could have a little bit more speed and range but compared with other manufacturers still ok.
For example: NTP time server doesn't work, can't send to syslog or SMTP server on LAN ports.
NTP server works from Internet as this device is intended to be a internet gateway.
Sending to a syslog server works too as long the syslog is in the same LAN as the DIR (Using the free Kiwi syslog here to monitor all my devices).
It can't be used as a router on a LAN...
Yes, it's a SOHO internet gateway with NAT/PAT.
It does its job here reliable. If you don't need 5 GHz radio, think of the DIR-655. It will give you almost the same features besides the second radio.