Preferably a flexible "generic action" approach, where specialized actions (such as "EatItem" or "OpenDoor" or even "Move") are all derived from a generic Action class, have their own (perhaps even dynamic) action cost and (see http://journal.stuffwithstuff.com/2014/07/15/a-turn-based-game-loop/) maybe even a smart system for suggesting "sensible alternative actions" on failure.
Time and speed, even though the game will block for player input are also essential, if somewhat trivial in the simple first iteration I have in mind.
Preferably a flexible "generic action" approach, where specialized actions (such as "EatItem" or "OpenDoor" or even "Move") are all derived from a generic Action class, have their own (perhaps even dynamic) action cost and (see http://journal.stuffwithstuff.com/2014/07/15/a-turn-based-game-loop/) maybe even a smart system for suggesting "sensible alternative actions" on failure. Time and speed, even though the game will block for player input are also essential, if somewhat trivial in the simple first iteration I have in mind.