I finished it.
Have you ever heard of Andrew Plotkin's cruelty scale for adventures? This is a measure of how cruel an adventure is from the point-of-view of things like sudden-death and getting into an unwinnable state. The classic scale has five ratings: Merciful, Polite, Tough, Nasty and Cruel, with Cruel being the worst. I would rate your game as Cruel, as there are several ways to die without warning and it is possible to get into an unwinnable state without even knowing that you're in an unwinnable state. In Gareth's era, this was probably the norm, so he would think this is okay. In the modern era, this is unacceptable and your reviewers would give you a real bagging. In fact, I think most players would just give up very early and move onto something else, as there's about 10,000 adventures to choose from. This is a pity, as the game has some nice puzzles. It just needs a little more fine tuning. It appears that the rock, crystal and pickaxe are essentially red herrings.
It's getting late now, so I'll try to send you some more helpful comments tomorrow, as promised, although Adventuron has already mentioned some of the major issues that I was going to mention.
For a further details on Andrew Plotkin's cruelty scale, see: http://www.ifwiki.org/index.php/Cruelty_scale.