Are you using any maps in the texture slots for the params?
I wouldn't call this "photorealistic", but this is something I threw together just using a generic cloud noise texture from Gimp in various texture map slots on the material.
You'll want to use things like normal maps to offset the refraction as well as an albedo with an alpha (or detail maps) to add things like dirt. Experiment with all the maps on enabled params. You'll also want to use things like reflection probes and anistropy, too. The 3D Materials demo is a good place to start.
Some of these features are fairly new to Godot, so there's not a ton of specific tutorials around yet. I'd suggest trying glass material tutorials for other engines, and trying to apply some of their concepts to Godot.