You might enjoy Larry Niven’s “Known Space” series? It’s less one long story than many, many stories (some more interconnected than others) set in the same universe, but there’s a lot of it. Some stories are darker than others, but overall the tone is optimistic and the characters have their flaws but don’t suffer from the “stumbling from one flawed decision to the next one” problem.
I suspect some of the stories won’t have aged well, given some of them were written over 50 years ago, but Niven plays with a lot of interesting ideas, and I have never encountered a sci-fi author that writes genuinely alien aliens the way he does. There’s also lots of exploring space, futuristic cities, and alien landscapes.