I am a longtime user of MC and have used it for my extensive music and movie collection for whole house distribution. I have struggled with Blu-ray playback for many years and experimented with lossless .mkv files. I have been very happy with the results and have decided to standardize on the .mkv file format for DVD and BD. However, very few players are both capable of smooth playback and support all of the .mkv playback features, such soundtrack and subtitle selection and chaptering. I have had issues with JRiver MC in both areas. I have tweaked the video playback settings to improve .mkv playback (by searching the Forum) but still have problems with certain files (some other players I have tested play them fine). Also, it appears that MC does not support the other playback features I mentioned.
I am a big fan of MC and will continue to use it for music playback. However, I am no longer using it for video playback. I now use XMBC which plays .mkv perfectly and supports all the other .mkv playback features. PowerDVD played all .mkv files perfectly, including the problem files that other players had difficulty with but it does not support the other .mkv playback features. I would love to see MC improve its .mkv support so I can return to it for video.
A related, but different subject, is MC as media management tool, mainly movie files. I have always used another program to manage movie information: My Movies for many years and now Collectorz.com Movie Collector. This is not a problem with music files because the metadata is part of the audio file, which is not the case with video files. These other programs give me the ability to update and edit movie information and covers. The automatic information retrieval used by many programs including JRiver MC and XMBC often return incorrect results (especially for disk bonus material and movies with the same name but made in different years).
MC is a great program for music - the best. I hope that over the years it can be that for movies as well - for me, anyway.