Context of the movie (with spoilers)
The movie is basically about a company which gives you a "new life". It fakes your death in a plausible way and it gives you a whole new identity. A new chance for you to start a new life. The company heavily relies on referrals of clients. You probably know someone that hates its own life and it would give anything to start over. That's your referral!
Personal thoughts (with spoilers)
For the first 20 minutes, I was trying to figure out what was going on. It took a while, but eventually, it became clear what was going to happen to the main character.
First, looking at Arthur's life before the procedure: he wasn't in a household where affection was openly shared with his wife. The separate beds, the way he doesn't kiss her back when she tries to comfort him—it all points to emotional distance. But to me, the lack of affection comes from him, not her. He's the one emotionally blocked. You can see this even more when the "new" Arthur—now Tony—talks to her in their house, maybe trying to understand her perspective, or even himself.
From the start, he was skeptical about the process (which makes sense), and the company expected his transition to be difficult. But the whole point of the movie, I think, is that even after becoming Tony—handsome, younger, with a house in Malibu and total freedom—he still isn't happy. Once again, his life is being decided for him. He has to be a painter. He has to live in Malibu (first world problems). Even the people around him—his possible new love interest—were chosen for him. He's in a controlled environment because the company can't take risks.
Watching this, I kept thinking of that saying: Wherever you go, there you are. No matter where you move or how much you change your appearance, you're still the same person inside. The same fears, insecurities, and desires follow you. That's Arthur's real problem—and probably the same for all the other "seconds" waiting for yet another surgery, hoping this time it'll work. (It probably won't.)
The wine party sequence was interesting—it felt like Tony was having some kind of breakthrough. But it all crumbles after his cocktail party, when he realizes almost everyone around him works for the company, even his new lover.
I'm not entirely sure what happened to Charlie at the end. He seemed to want Arthur to succeed in his new life, maybe because their fates were tied together (Charlie was his sponsor). But in the end, Arthur's new life just became another man's death. The person who "died" as Arthur was probably in the same hopeless position before him.