Well the cool thing is, Matrix Online isn't as deep as games like World Of Warcraft and Everquest in many ways since the main focus of it is playing through the story based missions that are written. However, if you miss any of these, you get a history backlog of all the story cinematics to date, so if you go without playing for weeks at a time, you can still get an idea of whats going on.
Well as with most games these days, the detail settings are very tweakable so there's a lot of room for optimisation. To get it running decently (high/max detail) you'd need this kind of PC:
Athlon/P4 @ 2.4Ghz
1 GB of RAM
7GB HDD Space
128 Mb GFX Card (Preferably a Radeon 9700/9800, or a Geforce 5700)
Broadband internet connection
Hehe, I gotta mention though the Matrix Media Player, which allows you to play any kind of Windows Media Player formatted file in the actual game, hehe very cool:
Matrix Online Radio