This is a huge issue that XBMC owners ignore to my knowledge. They insist that the issue is not XBMC, but the fact that you are unwilling to get rid of your entire menu structure, extras, etc. because you are stupid and should be playing MKVs. Obviously, not everyone thinks that way, but it certainly is the way that I felt when I got into XBMC for about 5 minutes before returning to my Dune players... which are a long way from perfect but DO give me full BD menus and work for the only and exclusive purpose I got them for: Playing my BD ISO rips and other media content. For streaming I... Well I have AppleTV, but I also have a Roku which I haven't hooked up to try yet. I don't do much streaming, the quality just bugs me, and I'm happy to chill in front of my computer monitors for that with headphones on.
Anyway, while there are certainly a lot of XBMC/Plex users out there, and I really think that it is a good product for many, it remains the case that I have over 300 BD and 300 more DVD ISO files which I demand be played back by whatever I use, and the Dune players do it (except the newest model).
What's good? The Dune players have a solid remote control and were built around a 10' interface. They are fairly straightforward to connect to your network, setup to browse to specific files, and to start any supported file playing back.
What's bad? They don't have a native movie wall, and adding a 3rd party one isn't hard, but is tedious. Yeah, it just bugs me that I have to manually go out and load the cover art. No, wait, I just go to my PC and tell it to find new stuff and it does, but it seems like the Dune players should be built to support the media wall systems a lot better. Zappiti, Yadis, MyMovies, etc should all have native Dune support where they just go out at 3 in the morning and look at the network for new media. If they find some, they update, if not, they go back to sleep. Nope, you gotta do it yourself. Oh, and much like I've seen from other players, it can be kind of slow. Not a lot of horsepower behind the chip or the memory.
I am still searching for the 'perfect' media player, and it doesn't exist as far as I can tell.
The HTPC really stands out because you can build it so it isn't slow. I mean, good graphics is easy, and mostly not that expensive. But, a good processor and memory means you can make those suckers really fast and work well. But, considering that you can get a Roku and a media player of any number of varieties for under a few hundred bucks, it certainly isn't the worst way to go. It's just frustrating that there just doesn't seem to be a 'perfect' NMT product out there yet... Well Kaleidescape if you have the cash.