Interesting discussion... here's my €0.02:
One of the better "games" for memorising concepts that I've come across is an old favourite in EFL/ESL called half a cross word.
Half a cross word
(In my experience, I think it's better to have the instructions in writing so that learners can refer back to them at any time).
Put learners in pairs, one is A the other is B.
They both get the empty cross word:
To learner A, you give the words across, which they use to fill in their half of the puzzle. While they're doing that, they can think of the best clues they can to describe/define the words to their partner, B.
To learner B, you give the words down and they do the same as their partner, A.
When they're both ready, student A asks B for clues down to complete their half of the puzzle. And vice-versa.
Because the learners have to think for themselves about the concepts and how to describe/define them, and because it's for a social, collaborative purpose, i.e. a social game, they're far more likely to #1 - ensure that they understand their set of concepts really clearly, and #2 - remember the concepts that their partner explains to them; because it triggers particular aspects of our social, collaborative nature, i.e. we tend to be much better at remembering stuff that has social currency/value, e.g. something a friend or colleague tells us or discusses with us (Can't remember the specific research papers right now).
In my experience, most learners also find this activity enjoyable and engaging.
Implementing this in Moodle:
However, I don't think that there's an adequate module or plugin for doing this in Moodle. One suggestion: You can try the various synchronous and asynchronous communication modules that support groups or groupings so that you can pair off learners automatically. Then they can talk or write their clues and guesses to each other. If they do it in chat, then you can check what they've written. If they do it via WebRTC, Skype, etc., it's more difficult to check but the learners will probably do it well because they understand it's for their own benefit.
Another activity is the Glossary module is collaborative mode, i.e. learners can create and comment on their own and each others' entries. Having auto-linking on makes it doubly useful in that their descriptions/definitions will show up in future texts that they study on the course. The glossary module also support rich multimedia so entries can get quite elaborate if you have keen, tech-savvy learners.
I've found it helps to require learners to pick a fixed number of words/terms to define each so that everyone gets a fair share of the work to be done. You can also introduce peer-grading with a ratings system so that learners rate the definitions/descriptions their peers have written, e.g. allocate each learner 3 - 5 votes that they can give for the best/most helpful ones. Does that make sense?
You can imagine how motivating it can be for cohorts of learners to help and be helped by each other, however, not all learners are as instantly collaborative as we'd like to think and may take some persuasion and practice for them to "get it."
Note that in both activities, the learners are doing most of the work. When the learners "get it," the teacher doesn't have to do much at all.
I hope this helps!