I would add only 3 concepts for an easy determination of an aesculapian snake at "first look".
Very right observation from Bero about the "head shape" and "face expression"...
But think also of these 3 other things.
1) Dorsal scales of aesculapian snakes are almost always smooth and brilliant. Only once in my life I captured an aesculapian snakes with all dorsal scales heavily keeled, but this is obviously not the rule: sometimes aesculapian could have only slightly keeled dorsal scales on the second half of the body, and that's all.
So: the overall appereance of an aesculapian snake (in contrast with Elaphe sauromates) is that of a smooth, shiny and very often even "brilliant" snake.
2) aesculapian have elegantly slender bodies. It's not a case that the latin name is "longissimus"...
3) the position "en accordeon" is typical for many snake species, but it's extremely typical indeed for the aesculapian snake!
So, if you see a long, slender, shiny snake, staying in a "en accordeon" position (obviously if you are in the right areal for this species), you can be pretty sure it's an aesculapian, even if you don't have yet seen the "peaceful" expression of its smile...
I post here, as typical example, two pictures taken "in situ" of a big melanistic male "en accordeon" on a dirty road in Cres.
P.S. From the tail shape, it seems to me that your aesculapian specimen was a female...