Jriver is nice from an audio and video quality perspective. It's got good features and has a focus on high end quality; you'll get better picture and sound quality with something like Jriver over somthing simplistic like xbmc because Jriver supports MadVR advanced video processing (Jriver calls this red October) and has a plethora of great audio features to go with it. The internal audio and video processing in something like Jriver is better than something you get in a standard player freeware. You can obtain the same functionality (or better) as Jriver with some plugins and add ons with some freeware, but there is a little more set up involved. Currently MB3 Theater supports MadVR, reclock, Vs filters and LAV audio so that's probably the most direct comparison to Jriver on the freeware side of things. If you wanted to use something else you can set it to use an external player and then use MPC-HC as your player (which supports madvr). There is a really good set up guide as a sticky in the top of the HTPC forum; Advanced MPC-HC Setup Guide
The reason people don't like Jriver is probably because it's not free. It's paid software. Also it's not a slick as the others and lacks the eye candy aspect a little. (xbmc and mediabrowser3) If you really want to make it look and feel awesome and show it off Jriver can't hang with XBMC or MediaBrowser3; they are just cooler looking on the big screen and have a lot of extra features. The trade off is a tad more set up involved, but there is guides to help.
If you want to do more than one room you'll want to design the system a bit differently. A lot of people want a media server but want to use it to enjoy their media in many places and on many devices. In my house my media server doesn't just feed my dedicated HTPC, it also feeds a couple cheap and easy to set up ROKU3 boxes where we use the Mediabrowser app and PLEX app on ROKU to browse movies and tv shows and playback in other rooms. I also use my ipad3 often for viewing, or to browse the library as a remote control. My Flexraid server feeds my brother at his house and also my parents, and I have it set up to stream on my laptop/phone/ipad when I'm traveling. I love to be able to sync content locally too so I can use it without wifi like on a plane, then with a couple clicks on ipad I can delete it and sync something else for the ride home. This is simple stuff I'm talking about, the core features are built into plex and MB3; you don't need to go to school to do it or set it up.
This is where things have changed the most recently. Before people were only concerned with single room solutions, and that was easy. The most popular option was probably just buy a NAS box and feed something from it. It works great. But the problem is a NAS box is dumb, it's a dumb (dumb as in it's only purpose is to serve data) little server box that's weak and can't do much other than serve data over LAN. It's not a good option for feeding a tablet over wifi, a ROKU in a bedroom, a streamer HTPC in the theater, a few friends, and content over the internet for traveling. You can kind of force the issue and functionality by having it feed a more powerful HTPC and having that HTPC do the rest of the work, but in hindsight you'd have been better off just building an all in one or a dedicated media server that was better suited for the tasks.
There's nothing wrong with the simple approach of xbmc off a NAS box for a single room, but I think a lot of people start out with that mentality and then discover and learn they actually want more. It's like anything else you get sucked in. If you can make a list of the must have features, a list of non priority like to have features, and clearly identify the list of do not need features it will greatly help you choose the right solution for your budget. Getting the wrong solution initially and then piecing together a less ideal solution with what you are working with is less desirable and upgrading or replacing stuff prematurely ends up costing more money, more time, and more trouble in the long run.
A DIY solution is also much cheaper than a MFG made solution so that's an area of cost savings without a performance compromise, or giving up functionality. In most cases it's more powerful, has more features, more performance, and costs a lot less. NAS boxes are overpriced significantly and it offends me. You can reverse engineer one or DIY for $200, but they charge $999 or more for the same thing. NAS boxes under $1000 are pure crap too. You can't really get a NAS box that does transcoding, especially under $1500, while in comparison an all in one unit for $1000 is really nice, or a more advanced HTPC + Mediaserver combo for the same price of $1500 is spectacular. PC hardware is both cheap, and very powerful. A $35 Intel CPU is more powerful than 99% of the NAS boxes on the market. You just need to put it together yourself, which is often the sticking point for most folks.
I think the main difference between solutions now is the recent trend and emergence of a "server" program and a separate "client" program. This has really shaken things up. Before you could do a simple NAS box or streamer server (low cost, low power) to feed your client and run something like XBMC which is everything in all one and made for a pretty nice single room solution. The trouble is if you pause a TV show because the kids are crying, and then want to resume it in the bedroom - or you want to know how many episodes of Season 2 you've watched and what episode you are on now - it becomes really complicated because each room is it's own solution and they don't function together as a unit or single device divergent solution. That is why the "server" programs have gained so much in popularity and functionality. With more advanced solutions like PLEX or MB3 you have a "server" program that runs on your media server. This program manages your meta data and library, is your organizational hub, and it feeds all your clients. It makes it easy to watch on the ipad, then click a button and pick up from the same point on your ROKU. Or use your ipad to browse your library and then play back on your theater screen, or use the tablet as a remote. You can share servers with friends, sync content for local playback, and set up remote video streaming while you are away. This is easy to do when the functionality is built into the platform like with PLEX server or MB3 server. If you watch something it's easily kept track so if you watch Season 3 Episode 6 on the bedroom ROKU and you want to watch the next episode the next day in the theater you don't have to remember what episode you watched, the theater system will show you the last watched episode even if it was on a different device.
The bottom line is you can take things really far, or keep them really simple. You can go MFG made and save the set up trouble and keep things simple, or you can go DIY and gain a lot of additional features and functionality while saving costs. You can go anywhere in between. I think the best solution for someone starting fresh is to plan for or spec out a solution that will allow you to take things far, this doesn't cost that much more $ and in comparison to a MFG made it's way cheaper. Just because you have a solution of system that can let you take things far doesn't mean you can't initially set it up to be very simple like a one room solution either. I'd avoid under estimating your desires if possible, I did that and I upgraded my HTPC 3 times, my desktop 3 times, and my server 3 times since 2010. It was fun and I enjoyed it, but I am not sure folks that don't share the same hobby would like it as much as I did. I thought initially I was doing great with a $200 HTPC and a $250 Flexraid server with cheap parts but I ended up replacing every part so in the long run it cost me more money than if I just went with a more advanced solution up front.
If you want a few good links or threads to get started let me know. I think this one was pretty good recently talking about "overkill" on HTPC vs not enough. Lots of viewpoints from different people so it might give you a good idea of how serious or how simple you wish to make things. Who else has built a ridiculously overpowered HTPC? What's your story?
If you want some picture examples of the difference between basic video playback and advanced video playback with MadVR, or you want to see some screen shots of picture quality differences this thread has some good ones: **** So you've built your HTPC-NOW WHAT IS NEXT ?? How to get the "ULTIMATE" picture and sound quality from your HTPC !!!! (MADVR? SVP? XBMC? Mediabrowser? Jriver? )
Larry M from this forum (firepower theater) did a HTPC build that was a nice all in one solution (media server + HTPC) earlier this year you might want to check out Critique my HTPC build plan
If you want some cool ideas about different front ends and configurations you can check this out: HTPC FRONT END SHOOTOUT: Show us your eye candy !
Just don't remind me I never posted up my updated screen shots, it's on my to do list for a long time but with the twins birth I seem to find a million reasons not to do it. If you want modern MB3 screen shots you can check out the MB3 forums, the project has really improved and changed a lot since that thread started. http://mediabrowser.tv/