ILikeBeans
It's been a while, but if I remember correctly turning and looking in a certain direction from random places on the map would cause large frame drops.

I recall that as well.  It was very bad right after release, but they patched it up somewhat.  There were still lots of area's outside where there were big drops in FPS as well as the fast turning drops.
 
It was still a fun game if you could overlook the dips & some of the other bugs.  I played it through several times...