Both games are good, but Final Fantasy 7 is the only one I have played for any decent length of time.
I tried to get into FF13, but it fell short of my expectations and I got bored.
No offence, but have you ever heard of Quake, Unreal Tournament or even Goldeneye for the N64? They were the same as Call of Duty (multiplayer FPS games), only better for not being mainstream.
Have you checked the Mystcraft wiki? There is a lot of help for writing stable ages there.
If that doesn't help, I am sure someone with vast knowledge of Mystcraft will post here soon.