I haven’t read Vances, so I’m afraid I can’t help specifically, but if you’re looking for fantastic sci-fi with subpar endings, I strongly recommend Iain M. Banks.
I’m not being flippant. I love those books, and Banks has an amazing grasp of setting, world-building, and creating fantastic characters and situations… and the endings are all mediocre to poor.
Still, worth a read.
Other than that, classic sci-fi I love includes Pournelle/Niven (“The Mote in God’s Eye”, and the sequel “The Gripping Hand” are both good, but I suspect the others they worked on are probably pretty solid as well), the “Lost Fleet” series by Jack Campbell, or anything by David Brin (the “Uplift Saga” Book 2 is particularly amazing).