As others have already stated, Roach's music has passed through too many phases to isolate to one or two "starting points." He's done minimalism (Quiet Music et al.), ethno-tribal (Soma et al.), dark ambient (Well of Souls et al.), drone (Magnificent Void and a ton of his more recent stuff), Berlin school (Empetus, Stormwarning), fractal EM (Blood Machine, Core), and music that can't be defined (Midnight Moon et al.).
But, if I was pressed to recommend ONE Roach CD to initiate someone to his music, it would be World's Edge because it is the best possible snapshot of his multitude of styles, except his overt EM stuff. Or you can try On This Planet which, during it's album-length track, also encompasses a variety of styles. The thing with Roach is this: He is so prolific and is so varied that you simply cannot judge him on one style or a few albums. I am nowhere near as enamoured of him as others here (to say the least), but even I can't deny his greatness of talent. I may not care for all his music but the man can certainly compose and play some amazing shit.
My personal fave, though, is Soma (his second collaboration with Robert Rich). This is about as close to true 100 percent perfection as I have ever heard in the course of thousands of albums. It is stunning...it literally personafies an entire genre (ethno-tribal) and, IMO, is absolutely without a doubt the most sensuous album ever recorded. If you can't get horizontal with someone you dig with this music playing, one of you has no pulse.