Yeah, it's weird that someone already invested in the show wouldn't think this is a very strong season. 50 Shades of Draper (shudder) notwithstanding.
The show stopped being just about Don by the end of season 3 I think. But if you do watch the show JUST for Don yeah, I can see how the show would start falling flat.
Don't watch Season 7. Don probably won't "lose", but he will be falling into the grave he's digging for himself. Best case he moves to California (I SAY KENTUCKY), re-centers himself, and lives as happily ever after as Don is able to live. Worst case he stays in New York, Burt retires Roger dies, Don becomes a mega-rich "successful" husk of a man -- estranged from anyone who ever loved him (Betty, Megan, Sally, even Peggy), alcoholic and philandering with no joy in life, and no longer even tormented by the lack of it.