Me, I really love Season 3 and I've watched it several times and still watch random episodes here and there, often totally out of order. I have the Blu-ray set and I just pull out any disc and play it sometimes.
One interpretation that's dawned on me over time is that the reason why Cooper is who he is in Ep. 18 is because when he "manufactured" Dougie to go back to Janey-E and Sonny Jim, he made him out of his warmth and his capacity for love. That's why Cooper is so cold and distant in the finale.
In TP, tulpas and doppelgangers aren't just clones, they're a PART of someone and they lose that part of them when they split off.
It fits with Mr. C and his "manufacture" of the original Dougie, too. Mr. C created Dougie out of vices. The original Dougie has a gambling problem, is into hookers and has a potbelly. He's into unhealthy indulgences. By contrast, Mr. C has no discernible vices, except maybe violence if that counts. He doesn't do drugs or even have much interest in sex. He's clearly sleeping with Chantal and Daria, but it comes off as more about power than desire.