This is a Twine game where you have three hours to learn the lead role in the Scottish play...only it's a wacky heavy-metal musical version with pyrotechnics and a flying harness.
Thus ensues budgeting the time you have to learn as much of the show as you can before the curtain goes up. You can't choose everything, so there are decisions to be made: Should you polish the lines, should you learn the music, do you talk to other actors in the show, should you make sure you eat or is it really important to make sure your costume fits?
Then the show begins. The choices you did and didn't make help or hinder you to fumble through the entire production. This is accomplished with some nice text effects and timing. The game assists you with the stuff you rehearsed and leaves you flailing for what you didn't. You can learn the show by memory a bit on repeated plays, and it's possible to get a standing ovation - or be taken out in an ambulance.
This is a great use of Twine, a lot of fun all around. The author has obviously been through this before, and a lot of the situations ring true. When an understudy is thrown onstage at the last minute, there really is a lot of triage: "Just stand on the side instead of learning the dance, because it's more important we take this time to teach you how not die by getting eaten alive under the turntable during the set change in this blackout..."
Having actually lived through similar theatrical shenanigans, including being part of a concept recording for a Macbeth rock musical, I can tell you Understudied is an absolute blast.