The main problem with Front row as I see it is that it relies upon Quicktime to play media. You can improve quicktime by installing Perian and the WMV extensions, so you will be able to play avi, etc. Not mkv files, though.
However, the main limitation is that quicktime only passes through AC3 from DVDs and from m4v files. Thus, if you have, say, an avi file with a 5.1 AC3 audio track, quicktime/front row won't pass it through.
In that case, you'd want to use something else, like VLC.
Now, the problem with VLC is that you don't get the beautiful interface.
If you want the beautiful interface and to be able to play everything, install the free Plex.
Now, the problem with Plex is that there is a bit of a learning curve to figure it out and get it to see all your media.
If you want it to be easy and see your media by itself, use Front Row.
Now, the problem with Front Row is....