Although fun(ish) to watch at times, and visually dazzling at others, this is one of the most poorly written and thought out movies I've ever seen. It tries hard to be edgy when the final result is just cringe, the character introductions play out like a toddler trying to tell a story, and their solution to the problem in the movie, as well as the reason they need the solution in the first place, is not convincing at all.
Margot Robbie does a good job playing Harley, and the visual design of Enchantress was excellent.
This extended edition adds some content to the Joker scenes. It doesn't add anything essential or anything that adds to the story, but if you're going to watch the movie you might as well do it right and get all the Joker scenes.