I've only got Enigmatic: Calling, and I fucking love it. Celestine Prophecy (which I'm listening to now actually) and Supremacy, Our Kind would be standouts for me, but there are no bad tracks on the album (although I never listen to Coming Home; for some reason I always skip it).
Heard a track off God's Equation the other day on a local metal show, Powersurge. I was there with my band doing an interview, and before it started I saw the DJ (I think that's what they're called??) pulled out the CD and played the title track. The drummer and I are big fans so we were pretty pleased. Then we were even more pleased when we managed to do the interview without saying anything stupid (other than me saying that the bass player was smoking crack instead of doing the interview). Good times.
I plan of course plan to get all the other albums, but what would everyone recommend I get first?