The Wizardry series is one of the earliest and most detailed RPG games system ever developed.  Wizardry had numerous classes and races, stats and skills and really focussed on character development.  This was one of the few series that actually encouraged you to transfer your characters from one scenario to the next and continue to build them up, rather than crippling them down to level one characters each time you started a new game.  In this way, each sequel truly felt like a sequel rather than just a new game with the same name and gameplay.  While it took them until Wizardry VI to really get out of the dungeon and make a truly epic game, it was well worth the wait, with VI and VII both being excellent RPGs.  While I-IV had quite crude graphics, with little improvement from one to the next, they were still fun to play because the strategic combat and intricate spell system were challenging and mapping out the dungeon was exciting (at the time...).  And you had a sense of accomplishment each time you came out of that dungeon, a little beaten and scratched, but with the knowledge that you had a little more experience and would do a little better next time.  Needless to say, many people became quite attached to their Wizardry characters.  Wizardry games came in really cool boxes (see pictures) and worth noting is that IV is perhaps the first game where the player takes the role of the bad guys, and an interesting twist to the usual kill-the-bad-guy dungeon romps.  Many of the "good heroes" which were enemies in this game were actual Wizardry characters which had been sent in to Sir-Tech over the years for one reason or another, so that's really neat.