Better question: What makes a good learning experience?
This is not a Moodle-centric question!
Bad usability - scroll of death, dead links, poor navigation, too much graphics.
Tools are limited - so need the appropriate tool for the task.
Standard themes, simple conditionals, mostly standard modules - KISS
Importance of scaffolding so learning is given clear direction, resources and assessment that is appropriate, meaningful and challenging to the learners.
What makes an expert teacher is feedback! Particularly from student to teacher or peer feedback/assessment.
Content must be relevant: the solution to the problem of information overload! Can release things at different times! 'Just in time'
Nice - Random glossary entry block feature in Moodle 2 where you can take a random entry from a glossary.