Pre-crash, the lives of all the charcters did suck. Jacob said as much.
This alternate reality shows their lives to be better, for the most part.
Only for a few, IMO. Jack's life seems to be better -- he has a son, whom he has (re-)connected with. Miles' life seems better, certainly; Hurley's, definitely. Sun & Jin -- maybe; they aren't married, but they are together. Claire's life seems slightly better, in that she's met her father's family.
But Kate? Still a murderer, still wanted. I'd say Sayid's life is worse than it was before Oceanic 815 -- without Oceanic 815, he wouldn't have become Ben's assassin, then Locke Monster's, or felt it necessary to blow himself up. Sideways, he's a murderer anyways, and still doesn't get Nadia.
Sawyer's life -- well, he's a cop rather than a crook, but he's still haunted by what happened to his parents. He's a better person, I'd say, but he doesn't seem any happier.
Locke's life -- seems like a wash; he seems to have gotten along with his father in the sideways-verse, rather than being used and abused by him. But he's also responsible for said father's current state, which has clearly tormented him.
(Oh, and since Locke's dad was the original Sawyer, his condition means that Det. Ford will never get the closure he wants. There's no likely way he'll ever even find out who Sawyer was, barring Desmond ex machina.)
Daniel isn't a scientist, and didn't seem really happy about his life in the brief bit we saw of him.
Charlie's life wasn't better before his near-death experience showed him the "other side", and I'm not sure he's better post-OD.
Ana Lucia is a cop on the take. Libby's in a home. Ben is a wimpy teacher.
Alex & Danielle do seem better.
Most of the other Others & Widmore's crew seem to have ended up as gangsters.
Desmond, pre-near-death-revelation from Charlie, was employed, but I'm not sure how happy he really was. While he wasn't stuck in the hatch hitting buttons, he also had never met Penny.
Juliet is an FBI agent, but her son is mixed up with the aliens invading her planet and she's secretly a member of a "terrorist" group, so who knows how long she'll stay a Fed. Oh, wait, wrong show.
I don't know that I'd say they are all better off in the sideways-verse than they were before they got on Oceanic 815. Some yes, some no, some eh.