Retroarch is one of my favourite software projects. I really like the philosophy behind it and I think the team have made great progress over the past few years. (Of course we also have to acknowledge the great work done by all the individual emulator authors, without which RetroArch wouldn’t exist).
Having used the software for so long I have come to understand all its arcane configuration details (i.e. Video settings, Input configuration, Shaders, Cfg overrides, Core options, BIOS requirements, etc.), but at some point I would really love to see a concentrated effort to improve useability. There have been some great strides towards this, but I feel that for new/casual users the interface and its myriad of options is still overwhelming.
There needs to be better documentation, a better initial setup experience (perhaps a wizard?), better update mechanisms (e.g cfg migration to newer versions), better in-app help, etc. I think once these things are addressed in earnest, RetroArch will gain the widespread adoption it deserves, rather than being relegated to the domain of only technical minded users or people with lots of time and patience to figure it out.
I realize there are other related projects that attempt to make it easier on the user, but I believe that ultimately RetroArch would benefit strongly from this approach as well. Look at the insane polularity of the NES Classic as an example; take some classic games and wrap them in a clean and easy to use interface and it takes off like wildfire.
Anyway, thanks to all the volunteers who have devoted their time to RetroArch/Libretro; we users can be picky and demanding sometimes but it is only out of our true enthusiasm for the project
(EDIT: Just wanted to add, i currently use RetroArch on a Windows laptop, a Mac Mini, a PS3, a jailbroken iPad, and now a Wii U as well. Simply amazing!)