I don’t think that Don is supposed to look bad, so much as dissolute. His hard drinking is catching up with him, and the bloom is off the rose.
Also, he (and Jon Hamm) is older. That’s what happens when you get older, alas.
Yeah, I thought that but it didn’t make it to the keyboard. I think Don still looks sharp (when he dresses up, not when he’s half in the bottle watching Little Rascals), albeit ten years older. But he’s 41 in Mad Men – right? his fake 40th was last season? – and as a 41 year old male I should be so lucky as to look that “fat”, “soft,” “pudgy”, “jowly” or whatever 
Great post; I find most of the MM commentary here a little glib and kneejerk, so thanks for such a thoughtful post.
I don’t think anyone denies that Jon Hamm is very good looking. But he’s such a good actor, he makes it believable that Don Draper isn’t always so attractive these days. Half the time he’s a sweaty mess who looks like he reeks of booze.
I’ve been watching this thread in order to come back and admit that I was totally wrong about Don’s big plans once he got his foot in the door.
FWIW though…you are totally wrong about Don being a total asshole. He’s a man of his times.