I hesitate to say this is the greatest song Dylan ever wrote because there are so many others one could point to, and at some point it really is just a matter of opinion.
But this song is so hauntingly surreal, the imagery so flashing, original and brilliant, the simple Blonde on Blonde arrangement so powerful, that it still sends chill up my spine after nearly fifty years. I've listened to it so many times I know every word by heart, which is either a tribute to a magnificent piece of visionary poetry, or else a testiment to my own obsessive nature. Probably it's both. :-)