I just finished level 18. This actually ends up being a pretty fun game once you get over the frustration of trying to figure out how to place the fault lines. It's an interesting concept and I'd like to see more.
1) You really need to clearly explain how the direction of the fault line is determined, I think that's turning a lot of people away and you probably lose more players on level 2 than anything else. It took me a solid 5 minutes to get it down, mainly because even when you figure it out:
2) The fault lines don't always spawn in the right direction. Sometimes, even when you get the right angle down, it'll position the line a little ways off. Definitely want to fix that or widen the angle you can turn the fault line. It really screws with your head when you're first trying to figure out how to place the fault lines. I don't know exactly how it happens, but it *seemed* to happen more in the upper sections of the grid.