Those stats sound good.
I'm wondering if it should be Huge...
Do we want to stick with the 90% spell resistance, or switch to the more common immunity to magic?
Sure. Vulnerability to sonic may also be appropriate.
Updated.
Yeah, I agree it needs something else. The original text mentions "its brilliance is too great, nearly blinding you", so maybe we can run with that?
Well I have no real objection to going a full size step, but in that case we should consider boosting the Strength the full +8 instead of +4...
I don't care for that (or the shatter vulnerability). I'd prefer for it not to have such an obvious flaw.
Blinding Brilliance (Su): Once every 1d4+1 rounds, a diamond golem can produce a blinding flash of light as a free action when it is illuminated by a light source. All creatures within an 80-foot radius burst of the golem must make a DC X Reflex save or be blinded for 1 round [Y rounds?] then dazzled for Z rounds, creatures that make their save are merely dazzled for 1 round. The save DC is Constitution-based.