What you mean by "excellent song"?
A good guitar sound, voice, atmosphere, rhythm? Of course, all elements are essential, but if you had to choose-which element would be the first in the chain ?!

hmm very good question!

I would say the overall feel of it when I finished listening to it, but I know that's a little vague.

Probably to be more specific maybe the chorus is the climax and it has to be satisfying...

Yes,chorus, I would agree with you

for me it's all about a consistent, solid melody and a great chorus.

If it stays in my head and draws my attention, it's already a good song!

Usually, I listen to the chorus and then the way the song gets there - I mean, a good song has a nice way of building up to the chorus as well

Personally, it's Melody first.....something that makes a non guitar player/musician be able to remember the tune.....

Very good question. I would say mix of how all those factors fit together.
If I had to choose one - I would say awesome vocal melody.

You know what maybe melody is first. As soon as the melody starts it has to grab you, so I agree with Jax and Bogdan