I don't know what the assembly cut is, the Alien Quadrilogy Blu-ray calls it the restored workprint version, and I thought it was very good. Although, I've always liked Alien 3, even the theatrical version. When I saw that I thought, "Wow, Alien, but with fucking amazing Shakespearean dialogue and English actors. What is not to like?". As an adult, I can appreciate the coherency behind a movie, and it isn't anywhere near as good as Alien or Aliens. But I still like it, and the workprint version deals with some very important plot holes, gives more time to the characters, while also improving the ending.
If you'v seen the workprint and still don't like it, then fair enough, your opinion is valid - this is the Alien franchise we're talking about, and it is acceptable to demand perfection.
EDIT: Just found out the 'Assembly Cut' was retitled 'Restored Workprint' on the Blu-Ray. They fixed some audio problems.