As a counterpoint to Alexandertnt, I like tropes. They serve as a carrier wave, the modulation of which can be really interesting.
Like Star Trek, with its elves who are repressing baser urges (and have siblings who embraced them). Which was so popular it got carried into the Warhammer universes, now that I think about it.
When a work of art tries too hard to be unique, it's can be exhausting. Art needs to speak to ideas which resonate with us. It's great that Avatar had tall blue aliens with MMI tentacles, but it resonated because they were like indigenous humans (also, they looked like sexy humans).
There's a ton of crappy novels where the author invents a dozen unpronounceable words for the various castes and social groups of various aliens, and it's hard to follow and it's hard to tell if there's any payoff. Being incomprehensible can be a replacement for actual depth.
Kinda like Homestuck, except there it does pay off. Mostly. And also largely because the various "alien" conventions are actually things we empathize with, we just don't have names for them. Like hating someone so much you're eager to interact with them, just for the rush.
Morrowind is an example where the main themes really were alien, and yet it worked. Because the developers weren't just making a crazy world, they made an exotic one... Really impressive.
Fakedit: Gonna read Neonivek's post properly later when I can