The Best Game Ever.
You can pick up a copy on ebay for nothing (20$ if you are patient).
In the dorms I had several new players in my group, the first thing I did was play through 4 missions of HQ. It works wonders with teaching the dungeon crawl "mojo." I had new players making maps, checking for traps and geting tactical in combat in a way that made the "vets" in the group look like newbs who taged along for the ride.
So abslutely recremended. It can bring that bit of dungeon wonder back into a vet group like nothing else.
Another selling point is that it is D&D in a box. Everyone is tired and grouchy? S#rew it, call for pizza - put on some pink floyd - pull out heroquest. Draw straws for the GM and relax, no.. chillax.
Here is some retro goodness.