When I say realistic, I really just mean interesting visually and conceptually. I need to get back into reading, but all of the books I've found with sapient and diplomatic aliens in them only have humanoid ones or "godlike" aliens with no real form. In a perfect world, I'm looking for something that has multiple distinct and thought out aliens like Becky Chambers' Wayfarer series, but with designs and backstories as fun (or funner) as Animorphs or Space Opera.
But really I just want a story on an alien world that isn't almost completely barren or taken over by humans. Or honestly any book where an interesting, alien species that isn't humanoid or just big evil bugs plays a fairly large role, and we get to see some of their culture and how they work.