The first open ended game that genuinely succeeded in creating a world worth your time to explore.
Morrowind was probably the first truly open ended RPG that succeeded in filling in every inch of landscape with something poignant, something imaginative, something scary, or something curious, that was worth spending the time to explore.
Even better, the more you were willing to explore the terrain, and the more ruins you uncovered, the more NPC's you talked to, the more sidequests you did, the more fulfilling the main story became.
As an action RPG, the combat system was the most obvious flaw. It was very one note, and repetitive. But, honestly, who cares? This game was so full of things to do, people to talk to, quests to finish, stories to uncover, and along the way, every step along the path, whether you follow the beaten one, or pave your own along the way, leads your character closer to his ultimate destiny.
Morrowind was possibly the most complete game I have ever palyed. After a 50 hour first play through, I started a second campaign, and played that for well over 80 hours, trying to do more sidequests to uncover more about this wonderful world, and it's very complex and engaging story.
It does take some patience to get into, though. At first, the lack of a corridor leading you to a certain destination makes the openness a little overwhelming. It's kinda like being dumped in the middle of New York City with five bucks in your pocket, wondering how long you're gonna last.
Though, one sidequest later, a new weapon upgrade, and a strider ride later, and you're set on your way.
As tedious as some sidequests might seem, they are not given for nothing, and unlike many, they actually uncover more about the world you're playing in, giving a contextual backbone to the main story. Dwemer ruins, yet no dwarves to be found? Three living gods, pilgramages to sacred places, vampires, and the return of a corrupted hero who was ruined by the power he was meant to protect from evil.
You learn about them all as you go. By talking to people, by reading books about them, by doing quests for people who studied them.
It's the most complete, most ambitious, and most imaginative world ever created a gamers willing to take the time to explore it. The story is enormous as the world it exists in, and eveny step of it feels complete and fulfilling.
Every time I play this game, I finish wondering what I missed. And after 4 complete playthroughs and over 200 hours of exploring this world, I'm positive there's still a couple things I never did find.