If you haven't listened to the Braga and Moore commentary on the Generations Bluray you need to. They go in to detail about everything that went wrong with GEN. Off the top of my head I can list a few things.
1. The script that became GEN was never completed. It was just more complete than a script by another writer who was commission to write a script without any TOS characters.
2. Interference from the Studio. Paramount execs mandated that GEN had to have 10 minutes of TOS in the beginning of the film and the TOS characters (Kirk) brought back toward the end of the film.
3. The Data comedy for also mandated by the studio. In a film about death and mortality, the Paramount execs wanted a comedy.
4. Klingons were another mandate by Paramount. Reason being is their notoriety in pop culture.
5. There was to be more action in the film. The transition from Kirk dying on the Ent-B was to be followed by a fire fight on board the observatory where the crew of the Ent-D found Soran. The Enterprise vs Romulans in a starship battle and shootout on the observatory. It was Jeri Taylor who suggested that the audience would find that boring, according to Brannon Braga. So the decided to do something off beat instead.
6. The Nexus was a convoluted device used only to unite Kirk and Picard. It's a device that Braga and Moore admit to never really defining on the commentary.
7. Other convoluted things like Picard having to crawl through a hole to get through a shield.
Why Kirk and Picard just don't take the Nexus back in time to before Soran launched his missiles (like back to the beginning of the movie when Soran was freely walking around the Enterprise-D).
How to isolate Picard and Soran on the planet. By kidnapping Geordi and then exchanging him for Picard to the Duras sisters but not before they beam him to the surface so he can talk to Soran. And a whole lot of other bullshit.
8. I'm sure most of you know that Braga wanted to destroy the Ent-D for the season finale of season 6. The Ent-D is casually destroyed for no other reason besides Braga wanting to do a scene with the sacuer section crashing on the planet.
9. Kirk and Picard making eggs. Not Braga's idea. He wanted Kirk and Picard to be fighting eachother or together on their respective ships. Moore and Berman didn't want to do what was expected with these two captains meeting so they went for something offbeat and uncanny.
10. Kirk's death originally being him simply shot in the back by Soran. Then reshot with a price tag of $6 million to involve Kirk falling to his death. With protests from the director David Carson not to do it and the studio ignoring him. Shatner told Berman, Braga and Moore there was no point for Kirk to be in this movie. Which according to Braga and Moore they countered, but Shatner rebutted their claims. Shatner agreed to have Kirk die because at the time he did not see a future for his character. That is to say there would be no more material/movies with the original characters. Braga and Moore admit their reach exceeded their grasp when handling the concept and the film as a whole didn't play up the themes they wanted to.
So yeah go watch the GEN commentary with them now! It's pretty funny in most parts. Also watch GEN with the commentary with David Carson and Manny Coto. They make the film sound redeemable at parts.