Hi!
It's normal, then. Originally, you had 120 GB of space, but now you only have 1.5... GB of FREE space.The thing is Mac OS X needs about 2-3 GB free for running as expected, then you need extra free space for your game ( see game specs for details).
I suggest you delete some files on your HD, which seems to be almost full, in order to have 4-5 GB of free space. Then, everything should be ok.
Good luck!