Ok, here goes...
What I like:
-- The MCC (windows message) commands. These make it easy to program a remote to talk directly to the window and not just send keyboard emulations to whatever window is active!!
-- Skinning is EASY!
-- Audio -- MC kicks any other apps butt when it comes to playing and organizing audio (including theater view access).
-- Pictures -- again, organization and playing of slideshows is awesome.
What needs improvement:
-- Skinning -- yep, it's easy, but it's not very flexible.
-- Plugins -- there's no way to develop a plugin for theater view (sure, I've seen some hacks, but I mean a REAL plugin). Look at... well, ANY other HTPC app for examples.
-- DVD -- DVD play sometimes locks up when changing modes (play / menu, etc...)...
-- DVD Menu -- When I send the DVD menu message, MC (instead of just going to the DVD menu) pops up an OSD. I have a widescreen projector, so I'm in "letterbox" mode when I watch movies. This cuts off the top of the OSD and makes it impossible to simply navigate to the DVD menu (I've created a routine in EventGhost to do this, but it shouldn't be necessary).
-- EPG!!!! Without an EPG, MC can't be taken seriously as an HTPC app. Nuff said.