WHAT WAS ALL THE FUSS ABOUT???

It's for people who aren't waiting for something to happen. Who have patience. Who understand that film is what it is, not what we may want it to be.
Maybe take a look in another few years.

I will start by saying I only caught parts of the movie on TCM. That said, here we go.

First of all, keep in mind the time period of the movie.
When the original BARBARELLA, (not BARBARELLA, QUEEN OF THE GALAXY), was made, it was rated "X". There were obvious cases of casual sex, drugs, and lots of other things going on, but not a particular topic that COUSIN COUSINE touched on; the two were distant(?) cousins, which some **frown on** as incest, or bordering on incest. (Consider the recurring controversy with Woody Allen, who married his wife's adopted daughter... not blood related, but...) It was also an affair between two married people, which BARBARELLA did NOT have.
Now, the more current release is BARBARELLA, QUEEN OF THE GALAXY which is rated "PG". Folks accustomed to that level of PG would/will be scratching their head about this COUSIN COUSINE.

I will guess that the Original Poster is American, and also comfortable with movies loaded with violence, explosions, gunfire, stabbings, beatings, and other assorted violence. European movies have largely left violence out of their movies, leaving the impression of a slow paced movie.
I have viewed a lot of non-American/Hollywood movies over several decades, as well as the typical Hollywood movies featuring sex, violence, nudity, and the Hollywood Ending (pleasant resolution).

What I have seen of this movie seems to be a "slice of life" sort of movie, which is typically not made by Hollywood because it isn't very popular...