The opening crawl should have explained why the Republic lacked a standing army capable of defeating the First Order and had to covertly fund the Resistance.

Poe Dameron should have died in the crash landing on Jakku.

I dislike the idea of Han Solo losing the Millenium Falcon for so many years and then appearing out of nowhere as a Deus Ex Machina.

Han Solo never thought he should put a tracking device on the Millenium Falcon in case it was lost or stolen?

The script would have improved if Rey had stolen The Millenium Falcon from Han Solo during her escape from Jakku and Han Solo had tracked her down to retrieve his ship. . . .

There should be no superweapon. The goal of the story is to find Luke Skywalker. Inserting a third Death Star is irrelevant to the story.

Finn should not have been a janitor.

Rey should not have been able to perform a Jedi mind trick. The other characters should have had to rescue her.

Kylo Ren should not have taken off his mask in front of Rey.

Captain Phasma should not have disabled the shields without a fight. . . .

Snoke should have a more menacing name.

Why did C-3PO have a red arm? This is never explained. . . .

Kylo Ren should have defeated Rey, who should have barely survived. . . .