no wifi->requires ethernet input, remote is not backlit, buttons on the amp are small and not backlit, can't dim the display
This unit, for its price, is a solid performer. It offers a bevvy of features that other manufacturers can't match for this price point. It won't go toe-to-toe sound quality (and power) wise with higher quality amps, but they have a higher price point to match. It must be clearly stated that the Onkyo 525 amp which replaces this model does NOT have powered Zone2, that is reserved for the higher priced (and specced) Onkyo 626. That makes this amp somewhat unique at this price point - powered Zone2.
The audio is quite bright, and the high end can sometimes be a little too under represented, and the low end is adequate for a unit at this price point. The Onkyo TX-NR515 also offers the ability to Bi-AMP, but this reduces the number of available channels by 2 (the unit is a 7.1 amp, and biamping reduces it to 5.1).
Network audio wise, the 515 is well featured. On the codec front, this unit plays an impressive array of formats. My high-quality format of choice, FLAC, is supported (full list is MP3, WMA, WMA Lossless, FLAC, WAV, Ogg Vorbis, AAC, Apple Lossless, DSD, LPCM*2, and Dolby® TrueHD). On my Samsung Galaxy S2, using the Onkyo Android app, I can stream FLAC songs on my phone (cover art also) to the Onkyo 515AE, and the cover art is shown on the monitor, as well as track information. This is fantastic, as the audio quality is non-lossy from the android phone, over the network, and digital all the way to the Onkyo NR515's TI Burr-Brown 192 kHz/24-Bit DACs. Therefore the source quality is fantastic. Streaming can also be done from PCs, MacOSX, GNULinux via DLNA over the network. Another bonus is that network audio streams can also be assigned to Zone2. Unfortunately HDMI sources cannot be rerouted to Zone 2 though! The Onkyo TX-NR515AE is a unique version of the TX-NR515 which includes support for Apple's Airplay. This is particularly useful for Apple idevices on iOS 4.2 or later. Furthermore, many non-apple devices (including PCs, XBMC, and others) also support Airplay sending now.
The main bug bears are the lack of a backlit remote, but as the android/iphone(also works on ipad1 and up) acts as a full featured remote, this makes up for the cheaper remote. Another problem is that you'll need to hook the amp up to a router or a wireless access point because it only has an ethernet port on it -- and this is something you should do as an owner, because the network features are a huge plus with this unit. Also, in a dark room, if using the front of the amp to select different sources, it can be difficult to determine which button to press because there is no backlight (however, the activated source is shown on the display on the amp, and on the TV/monitor).
One final thing I particularly like is Eco Mode (hybrid standby). This allows you to assign one HDMI source to be on a "hybrid sleep", such that the amp stays in a very low power mode and turns off all powered zones (1,2) and passes video and audio straight through the amp, allowing your monitor/tv to do the audio. This is useful if you are watching a TV broadcast and want to save a bit of power, as having zone 1 charged and ready to go will consume many watts of power (I have not tested a no-output resting state yet).
These features, and additional features such as Pandora, Spotify, and instaprevue, make this an easy purchase for the consumer looking for an amp for a family room area with a bit more fuel in the tank than a cheap setup from Samsung and the like. One thing I have not tested is the 4K upscaling, but this supposedly supports it and offers the unit a bit of future-proofing capability.
Bang for buck, with network features, powered zone 2, and the ability to save a bit of $$ on power bills, this is one of the best amps on the market for the price ($549 Australian dollars at purchase).