Should have made things more clear at the end...

Just vague allusions to the future and what is going to happen. I don't think people not familiar with the books would get that Leto is about to become the ruler and the set up at the end of the novel with him becoming the God Emperor. One simply watching the series would more likely think he's just going to disappear into the desert until he can find a way to die.

They could have explained why for example Leto's sister couldn't marry Farad. She just says that he can never be her husband and doesn't explain that it's because she's going to marry her brother. One unaware of that in the books might wonder who she is going to marry then and how that will impact the future. To be honest, I never thought that made much sense in the books given how things played out. It really wouldn't have made a difference if she and Farad were married or not. Leto could have maintained the same independence as he did throughout his 3500 year reign from their descendants.