...all good sequels must accomplish five criteria:
1. Give the audience something new
2. Identify what worked and build off of it
3. Change the stakes
4. Play with expectations
5. Add new memorable characters
Like Alien 3.
1. Prison Planet, Impregnated Ripley, Religious Themes, Total Nihilistic Tone and an amazing soundtrack.
2. Return to single Alien plot and gothic vibe. Action removed. Weapons removed. Family elements removed, etc.
3. First she fought for he life, then she fought for a daughter, now she fights for us all. Ripley is infected and going to die. She is running out of time to stop the company stooges who are personally on their way this time and fully capable of finally securing a specimen on their own. The odds that she will fail are real. She is surrounded by rapists and murderers, not friends or marines, and technology is extremely limited. There is little time and limited options. It's endgame.
4. I'm sure many expected a much different film and a much different outcome to her character arc after Aliens.
5. Clemens, Dillon, and Andrews to start. That's ignoring medium characters like Aaron, Golic, and Morse. Charles Dance, Brian Glover and Charles Dutton aren't memorable? Charles Dance alone is a superior presence, one I'm still shocked made it into the Alien Franchise. The man is legendary. Clemens was also the only person Ripley slept with during the series.
And no doubt this could be described in much more detail and with better examples by others.