"The best cheap addition to any home theater setup."4.5 starson by the_eternal_dark
Pros: Plays tons of formats, including the elusive MKV, smoothly at high resolutions. Modding is simple enough as well, which led to being able to read my ext2 HDDs, customizing the menu and backgrounds, and expanding the capabilities of this little gem.
Cons: The biggest issue I had was trying to find a another remote for this thing. The tiny remote is very easy for children and wives to lose in the couch. I went to Meijer near by and got a $20 Philips remote that has learning capabilities. Problem fixed.
Summary: Out of the box, this media player is a little clunky and flawed, but if you update to the latest firmware from WD, 98% of the issues are fixed. If you are like me and have to have support for something the factory firmware doesn't support, you can void the warranty and install a custom firmware, and allowed me to use my ext2/ext3 formatted external hard drives. It's quite simple and very safe. There has been very few video formats that I have not been able to play, and my favorite being MKV, is supported (for anime, I know, I'm a loser). You truly can't go wrong with this, unless you HAVE to go with a proprietary standard, such as WMV, which this little guy will always say no to, and could be a problem that some people here are having problems with but aren't reading the manual. As far as audio, I don't do much listening through my WDTV, since I like to listen to it on the go, but it does play many formats flawlessly, just in case you like to do so. I haven't tried viewing any pictures, but that is also why I have a digital picture frame. You can't go wrong with this little beast. Slap a couple terabytes of hard drive space loaded with AVI rips and MKVs that you have "found", and you'll be happy, just remember to make sure that you update the firmware as soon as you open the box or you may have some issues that are mentioned in other reviews (aside from those not being able to play unsupported codecs).
As for the firmware, I went with B-Rad's WDLXTV firmware, which adds tons of cool stuff. Note though, you can also damage your player if you are careless or mess with anything you have no experience in, such as advanced settings and other cool "high-level" Linux stuff. As usual, modding can void your warranty, and with any mods you do, no warranty is implied, enforced, or provided. Use at your own risk, should you go down that path.