I like that it's easy to use, even for novices! The user-friendly interface makes getting started quick & painless.
It also has great help documentation which can be very helpful when you're stuck or unsure of how something works. There are some minor bugs here n there but nothing major at this time. We've been using open docman since August 2015 as an internal version control tool with our developers being able to upload files into their folders (as well as read them) so they don't have to keep track of physical copies anymore.