"Who really killed Hamlet's dad? Can the Prince ever 'get' Gertrude, or is that just wrong? What does Richard III want with a horse anyway? And where did the gravedigger get that gorgeous pink dress? Avenge your father, defeat your evil uncle, and ascend the throne of Denmark in this faithful adapatation of Shakespeare's seminal work."
It basically follows the plot of Hamlet but there are elements from other Shakespearean plays mixed in as well, and it's full of little details that are delightful for us Shakespeare geeks - or at least I was gleeful all the time.
(There's a link to "help" under the game, but the "hints" link is dead so I felt like little something should be added.)
Your quest is to solve all the little puzzles in the right order. Basically you just type in directions like "look at portrait", "ask gertrude about claudius", "go north", "take skull" and so forth - you'll get the hang of it quickly. Talk to everyone and everything, try out even the craziest ideas, and when in doubt use "examine", it's probably the most useful command there is. Also, it's a good idea to always save the game before you do anything drastic - if your plan fails you don't have to start the whole game from the beginning again. (Just type in: save yournicknamehere, and when you want to go back to where you saved it type: load thesamenicknamehere).
& If you get stuck you can pm me, if you like - there are a couple of tricky parts, or more like so far-fetched that figuring them out is almost pure luck. I consulted a walk-through I found but that kinda spoiled the fun for me for those parts. So if you'd rather just have a hint than the ready answer, I can try to make one up!
I have to admit that this is kinda really old news (the game was launched in 2003), but I discovered it only today and wanted to promote it just in case there are others who have missed it too.