That's easy. Forgotten Realms: The Archives - Collection One, because of Eye of the Beholder.

I do have to say though, that this time I playied EoB with the All Seeing Eye (automap tool), which made the game even more enjoyable.
I just don't have the time to map everything on graph paper anymore :)

I'm throwing in with Eye of The Beholders, it was the only full price on release I bought this year and brought back the joy of map again.