This is the exact same though process I went through when looking - I would love to experience Stanford courses - but the single course being nearly the entire cost of the GT one...

I'm on subject #7 of the course this term - overall it has been a pretty positive experience, though you need to research the subjects you're taking on - OMSCentral is critical here.

I've so far avoided any subjects that require group work, and I'm really hoping to keep it that way.