I don't think a human-only universe can ever be as interesting as a multi-alien one.
It leaves too much creativity & potential on the table.
If we are truly the only intelligent beings in the universe - that removes something a little special from exploring space.
Except almost all multi-alien fiction just portrays the aliens the way you would a human, or very close to it. Most of them walk on two legs, or at least reason and act similar to the way a human would. Most culture shock moments are based off of actual culture shock when going to another country or talking to someone of a different race.
Klingons are space Arabs, Ferengi are space Jews. Romulans are space Romans that later got turned into space Russians.
Same with Star Wars aliens, unless they're just there to "look alien" and play the flute, which a lot of them seem to be. What are the Hutts if not fat slug caricatures of human mob bosses?
And there are all sorts of creative routes you can go to add strange beings to the universe without a single real alien.
Take a show like Red Dwarf - human-only universe, but set 3 million years in the future when humans are all dead. You have only one actual human on the show for most of the series. And he meets holograms, androids, simulants (think the blade runner androids, but more violent), and genetically engineered lifeforms.
Alpha Centauri before the expansion had one real alien: the planet, but factions like the Hive were more alien to the average westerner than most of the aliens on Star Trek ever were.
Firefly showcased the differences in class instead of racial differences. The Alliance was so far in advance technologically of the colonies that they were practically alien. And instead of Jawas hawking droids, you had old Chinese dudes. Instead of Jaba the Hutt, you just had a human crime boss who was rich enough to afford his own space station. And it all worked because the concepts for these characters are what "aliens" in shows like Star Wars and Star Trek were based off of originally.
Visually, sure, it's hard to beat seeing weird
green alien strippers or whatever. But in the end, a thot is a thot, human or not.
