5
easy to install, easily configured, use of plugins is fairly easy, clean UI.
There are some missing features I'd like but I can hold off since I've read some plugins are coming.
Other "webmail" products are complex, held together with string and bubble gum. I've spent days trying to get SquirrelMail and Horde working. Where as I had Roundcube up and running in less than 5 minutes (for each of their basic functions, that is sending and receiving email).