Created in 1988 by SSI, Inc. under a license from TSR, Pool of Radiance was the first computer game to bear the AD&D (Advanced Dungeons & Dragons) name.
Although there were a few minor flaws in the design, this game was the catalyst for the very popular gold box series of games from SSI.
Set in the Forgotten Realms game world, Pool of Radiance set your band of adventurers in the ruined city of Phlan, on the northern coast of the Moonsea. Phlan was being re-colonized, and the city council offered your party dozens of missions to clean out the monster-inhabited ruins.
The game design was ambitious in several ways. First, the non-linear gameplay was almost unheard of in a game of this size. There were tons of quests in the city and nearby wilderness, most of which could be done in any order you chose. Mapping was extremely simple, since every "zone" was a 15x15 grid, and was helped along by the coordinate display available in most areas. This was also a bit of a flaw, because once you had mapped an entire area, the areas you hadn't seen became obvious, and therefore it was too easy to find secret areas. Of course, mapping was optional, since in most areas, you were able to go into "map mode" and see a top-down map of the section the area you were occupying.
It was also innovative in that the combat mode was strategic in nature. When you entered combat, you would move to a vaguely isometric view (The rest of the game was in first-person static, like Wizardry), and be able to issue turn based commands when each character gained the initiative.
Top all of this off with a long and varied AD&D style storyline, and you have the makings for something that even SSI could not improve on in their later gold box releases.
While none of this may seem very impressive in light of more recent achievements in computer games, it was incredible in 1988. Not to mention, the game has so much replay value, it might even surprise you today.