I find this thread fascinating as I just took our company (we run 3 online schools) over to Moodle. One of our schools was already on it (using MoodleRooms, I moved it to our big cloud server), one wasn't using anything but a Joomla site (not much interaction at all except via email) and the third was on D2L.
I found the D2L structure confusing and disorganized. Some of this was due to an older, VERY non-techy person being the one who suggested D2L. He didn't fully understand it and forced everything into the discussions area. It was a gigantic mess. We're now fully moved to Moodle (after 80 hours of my development time) and the students love it, especially the topic/week setup (we're using the collapsable topics plugin).
Yes, we now have to offer our own support, but, we can pay to have mods made to the system instead of being locked into a hosted package stuck on the developer's time frame. We already paid the poodll developer to create a new video assignment function that dumps the video over to youtube (to save space on OUR server). It's PERFECT for what we need, and replaces the old "force the students to use dropbox to get the videos to the instructor" system we used with D2L.
I'm sure with time and training I could have figured out how to make D2L work better, but the whole "go to this tab for files, this tab for forums" thing was just terrible. Then the forums were ALL on one page instead of broken into week. I can't figure out how the students even managed on that system. They (and I) are much happer now on moodle