The serious people who deconstruct Mad Men have decided that Don Draper has become a bit of a bore (he has always been a bit of a boor, but that's beside the point). What with all the flashbacks this season to Phase II of The Worst Childhood Ever , the sometimes cloying, sometimes sadistic (and pathological) affair he's carried on with Sylvia Rosen and the utter indifference to (fill in the blank) his children, his wife or the well being of his employees, Don has, according to conventional wisdom, become a bit of a dick.
Even worse, so this theory goes, is he has become uninteresting. After all, we have known for a long time he had a "difficult" childhood  and his philandering is certainly no secret  but what the flaggelators demand from Don is some emotional growth, some insight into his behavior and a pivot to a better version of himself (or, in lieu of that, to die from lung cancer, hypertension or cirrhosis).
This is a curious opinion considering the people who follow the show the closest should know better than anyone that Don's core philosophy has long been known and it does not account for personal growth or introspection. The twin pillars of the Draperian world view are that (1) "people don't change"  and (2) that "people tell us who they are but we ignore it because we want them to be who we want them to be." 
Don has been telling us who he is from the word go, but the only person who figured him out was Dr. Faye Miller, who was astute enough to know that Don only likes "the beginnings of things."  And why wouldn't Don like the beginnings of things? In the beginning he is all those things that we want him to be - observant and attentive, charming and rakish, and the smartest guy in the room. It's only when the pesky details of relationships, be they of the professional or personal variety , begin to take root that Don's wanderlust kicks in.
To unpack Don's personal life, one need only look to the end of Season 4 for all the answers you need. After yet another close shave regarding his stolen past, Don opens up to Faye about stealing Lt. Don Draper's identity. They have the following conversation:
Faye: If you resolved some of your personal issues maybe that sick feeling will go away. You don’t have to be alone.
Don: And then what happens?
Faye: Then you are stuck trying to be a person like the rest of us.
After having this pearl of wisdom dropped on him, Don quickly asked a woman he knew almost nothing about to marry him. Way to go, Faye!! If springing a surprise proposal on Megan wasn't enough, Don also tipped his hand to the audience when he and Ms. Calvet had the following exchange:
Don: You don’t know anything about me.
Megan: I know you have a good heart and are trying to be better.
Don: We all try, we do not always make it. I have done a lot of things.
Megan: I know who you are now.
Um, you SO didn't know who Don was, Megan, but thanks for playing! Because, see above (people don't change, people tell us who they are ….). Anyway, that Don turned out to be just as big a louse in his second marriage as he was in his first is no surprise, so why do we really care whether he gets into weird S&M scenarios with Sylvia  or lingers outside her apartment?  Don is a philanderer who is incapable of intimacy with anyone he engages with sexually. The only two women he has bonded with emotionally are Anna and Peggy who, coincidentally, he hasn't fucked. That this season's flashbacks have picked up the story of his childhood after Archie's death just fills in the final blanks of why Don is unable to be anything other than a handsome cipher.
But for as egregious and odious as his conduct is in his personal life, the bum rap Don gets for being DONALD FUCKING DRAPER in the office baffles me. The reality is that when it comes to being the alpha male in whatever agency he works, Megan has it right, Don *is* Superman . Consider what Don's prodigious talent has secured for his co-workers:
- When Sterling Cooper is acquired by PPL, but for Don's lack of a contract, which he leverages to get the folks from PPL to toss Duck overboard, the team would be working for a wobbly alcoholic incapable of running an advertising agency. 
- When PPL flips itself (and Sterling Cooper) to McCann, Don hatches the plan to have Lane fire the partners. 
- When Lucky Strike pulls its account, it is Don who pens "The Letter," which starts the ball rolling with the American Cancer Society (and eventually Dow Chemical). 
- Speaking of Dow, Don's the one who gives one of his most lethal pitches to secure their business - an enormous account that helps ensure the solvency of the agency. 
- Oh, and if having Dow as one of your clients was not sweet enough, Don locked up General Motors too when he went outside the box and pitched a merger to Ted Chaough over drinks in a hotel bar. 
In other words, if Don Draper was a stock, investing in him back in 1960 would have resulted in a rather tidy return on your investment. He is now the creative director at one of the 25 biggest advertising agencies in the world with two of the bluest of blue chip corporations under contract.
And what of those co-workers who have profited so handsomely from the talented Mr. Draper? Peggy owes her career to Don's willingness to pull her out of the steno pool and promote her to junior copywriter.  Don could have shitcanned Pete years ago  or let him twist in the wind when the partners went rogue to form SCDP,  but instead, Don kept Pete close, he even put up $50,000 on Pete's behalf when the firm was in jeopardy . As for Roger and Bert, their fates would have been sealed had Sterling Cooper gone to McCann with PPL  and without Don's caches and genius, the partners could not have formed their own agency, meaning Joan would still be working (though no doubt quite competently) at the retail store Bonwit Teller.  So instead of lambasting Don, as Joan did after Don quit the Jaguar account , a thank you would be nice.
1. The deep dive into Don's upbringing occurred during the show's 3rd season, which was bookended nicely with Don's conception and birth in the season's first episode, Out of Town and his father Archie's death in the season's finale, Shut the Door, Have A Seat. This flash backing occurred well after the seminal Season 1 episode, The Hobo Code (Season 1, Episode 8).
2. His words. The Flood, Season 6, Episode 5.
3. Don's been sneaking around literally since the show started and, a brief period of fidelity in the wake of Betty's discovery of his affair with Bobbi Barrett and the first few months of his marriage to Megan, Don's been laying pipe with any and every brunette mother figure/whore in the greater New York City/Ossining area since on or about 1960.
4. The Mountain King, Season 2, Episode 12.
5. The Summer Man, Season 4, Episode 8.
6. Tomorrowland, Season 4, Episode 13.
7. As Roger noted, Don's problem is that he doesn't value relationships. Shut the Door, Have A Seat. Season 3, Episode 13.
8. Man With A Plan, Season 6, Episode 7. Don also engaged in some mild BDSM at the beginning of Season 4 with a prostitute, who he repeatedly asked to slap him. Public Relations, Season 4, Episode 1.
9. The Crash, Season 6, Episode 8.
10. Man With A Plan, supra.
11. Meditations In An Emergency, Season 2, Episode 13.
12. Shut the Door, Have A Seat, supra.
13. Blowing Smoke, Season 4, Episode 12.
14. Commissions and Fees, Season 5, Episode 12. Although it should be noted that we are not told that SCDP is now the agency of record with Dow until the Season 6 premiere, The Doorway.
15. Man With A Plan, supra.
16. The Wheel, Season 1, Episode 13.
17. Nixon v. Kennedy, Season 1, Episode 12.
18. Shut the Door, Have A Seat, supra.
19. Blowing Smoke, supra.
20. Roger did not even appear as a box on the organizational chart of the PPL-led Sterling Cooper (Guy Walks Into An Advertising Agency, Season 3, Episode 6) and the partners described Bert's post-PPL future as being "put on an iceberg." (Shut The Door, Have A Seat).
21. Souvenir, Season 3, Episode 8.
22. Man With A Plan, supra.