Bonus points first:
Game: Dark Mage
Back in the early 80's, during high school, my friend and I would dial into the University of Washington's VAX, and play Zork on it using his TRS-80. We spent hours mapping out the world, trying to work our way through it, but we could never solve it. We kept reaching dead-ends, and weren't able to figure our way through. It was only months later after he bought a commercial copy of the game did we find out the version on the VAX wasn't actually solvable.
Dark Mage is the closest you can get to Zork on the 2600. If you liked text adventures, I'd highly recommend checking it out.