Here's the best way to sum up their season: they added a 6 WAR superstar pitcher and didn't increase their wins by any this year.
I do think that the progression of young guys this year was generally good, so it wasn't an absolute failure of a season. Bart and Gonzales look like legitimate starters going forward with the hitters and Cruz put together a really good full season after his nasty injury last year. The fact that Cruz seamlessly transitioned to CF and put up good defensive metrics (+2 OAA in CF) is even better, I think they have their CF long-term. Skenes is obviously an ace and I think both Jones and Ortiz showed they're good starters as well, although I'm skeptical of how much of Ortiz's performance this year is sustainable going forward.
But beyond that, it's pretty awful. Even with Gonzales (2B), Bart (C) and Cruz (CF) locking up those positions, they still have huge holes or question marks at a ton of other positions. Reynolds is a liability defensively in LF, but you know his bat will play so it's not the end of the world. But beyond that, there are massive question marks or just complete holes between the rest of their positions. The development of the 6 guys above (Bart, Gonzales, Cruz, Skenes, Jones and Ortiz) is the only saving grace for how many other awful developments and regressions this team had.
Suwinski went from a legitimate platoon bat to a minor leaguer. Hayes offense fell apart entirely and it's pretty clear his back will never be healthy enough for him to be a good hitter in the MLB. De La Cruz was absolutely horrendous after being acquired, to the point where I think they should just non-tender him. Bednar became an atrocious reliever. The UFA additions Cherington made were all terrible. There was far more stagnation of regression than progression, even with the massive jump Bart made.
I don't feel any reason to be optimistic about this team going into next year because there's no reason to think they're going to actually do anything to improve the team substantially. Nutting is completely fine with this team being a mediocre .500 team, it's good enough for fans to show up and he'll be making a nice profit with it. This doesn't excuse the shitty job Cherington and Shelton have done, but I just don't see any reason to think that Nutting will actually push changes when the team now is doing what he wants it to do: make him money.