All about the storyline
For those not in the know with MxO, the game's most prominent feature besides the bullet-time combat was the developing plotline to the game. While certainly most MMOs include features of lore and backstory, MxO took that one step further by attempting to develop the story in real-time with the players. Originally the game featured a special division of developers, the live events team, to deal specifically with interactions between the players and the developers.
The events originally were designed only to support the main story, which was to be told through "critical misisons" which were introduced monthly. However, due to the game's stunning lack of static content, these events ended up becoming the backbone of the game. The events also branched out to tell stories of their own, such as the introduction of Neurophyte, a Zionite with "kill codes" for agents stuck in her brain, and the crew of the HvCFT Novalis II.
But, sadly, as the game eventually transitioned to SOE, the events team were the first to suffer. The level of player interaction began to evaporate as the game moved over to filling in the gap in their static content. Events became the territory of one single developer, Ben "Rarebit" Chamberlain.
Why the game didn't suck even though everyone said it did
Simply put, many people had subscribed to the game because they didn't want to sit around running missions (and eventual endgame raids, which really confused the greater player community.) People wanted to interact in the story, meet the characters, and actually deal with the social problems that erupted over different philosophies. For once in a game's life, the majority of players inside of it wanted to roleplay and deal with the lore, instead of shying away from it and playing the game just as a game.
There was no greater feeling in any game than dropping by Debir Court and running into The Oracle, feeding a flock of birds. She'd look over at you, give you a wave and let you sit with her as she spoke of the greater happenings of the Matrix and offered you a cookie.
I remember machine-loyalist players being called together for an organization meeting by their liaison, Agent Gray, and meeting downtown. Upon everyone gathering, Agent Gray called attention to multiple problems in the Matrix, before the tables were violently turned as The Architect entered the scene to call all the players to arms.