I realize that many hold in high regard games like Baldur's Gate and the D&D Gold Box games, and with good reason, but when I think about the pinnacle of my CRPG experience one game stands above and alone: Ultima VII - The Black Gate. The introduction to what, I suppose, was the third and final Ultima trilogy and its ultimately misguided arc that would fizzle out with the largely disappointing Ultima IX, The Black Gate was itself an absolute masterpiece from beginning to end. In my mind, the reveal of The Guardian through the static of my computer screen as the opening centerpiece of the game is one of the most iconic beginnings, if only because I associate it in my mind as the prologue of one of the best video game stories told.
The game is almost literary in its structure, set initially in the context of a murder mystery in the town of Trinsic, but eventually stretching into a grand epic across the face of Brittania. The world that you return to after a presumed 200 year absence is both exactly and nothing quite like the one left behind. Aside from the considerable technical improvement in the game's presentation, the presence of The Fellowship which has become the moral leaders of the realm adds a phenomenal layer to the already complex moral landscape of the series.
I'm not sure that a game world ever felt like more of an evolutionary leap from anything I've played before it that Ultima VII. It's certainly true that modern worlds are often more interactive and more complex that that of 1992's Brittania, but for the standards of the time this game's technical achievements are mind bending. For a series that had established itself with games like Exodus, Quest of the Avatar and the criminally underrated The False Prophet -- to say nothing of the Ultima Underworld games -- that it managed to top everything that had come before by an arbitrary factor of ten is proof positive that it is one of the all-time classics.