From my point of view Blackboard and Moodle are over kill unless your a school with very narrow requirements.
I've done a little worth with D2L thats not a bad middle ground for a SME, but Its kind of amazing how much you can do with wordpress and a few hundred lines of code, That said theres some really sold Off-the-shelf plugins that can do most of the hevely lifting.
The hardest from my point of view is hosting, and maintenance, and maby enrollment. We've had customers with 2-3k users with out and issuie, on wordpress, running on very reasonable hosting.
I think Phils got a demo site kicking around somewhere.