Ok, I'll try.
I think his music is very beautiful. And that does not answer your question, because beauty is in the ear of the listener, and many composers have written beautiful music. But I revere Bach above all the others because is important to me to understand things. How something works, why it goes one way and not another--this means a lot to me. (So much so that in my day job I am a scientist). And Bach has got to be the greatest teacher of music, ever. When I play/hear his music, I feel like he's explaining as it goes along how counterpoint works or what is the potential of the key signature. For me it is that extra layer of understanding that makes Bach special.
An honest, if dorky, attempt.
--s.