"The Dead Tower" is unusual in that while it works as your ordinary 3D terrain exploring game, the point is to explore the written word. So game mechanics? Check. Text based? Also check. Is it IF? If so, it's totally unlike most other pieces which one could classify as IF. While its atmosphere is evocative of a narrative, the game doesn't seem to have a distinguishable plot. But then of course, in this very way, "The Dead Tower" strongly resembles much of Porpentine's work, which is generally accepted as IF by now.
My only major critique of this game is that it is a bit difficult to learn to navigate.