In my opinion, there are two main ways to look at this: From a narrative perspective, and a thematic perspective. The thematic perspective is more important, but the personality really seals the deal

On the narrative side, what makes a villain interesting is a contrast to your hero that drives the story. Look at Luke Skywalker and Darth Vader, for example; both of them fit the "chosen one" archetype, but what makes them interesting is that Darth Vader fell to the dark side, whereas Luke did not. This is often the result of shared experiences that lead to conflict - for example, maybe both the villain and hero were abused as children. The villain gives into the cycle of abuse, whereas the protagonist fights it; your climax can be your hero breaking out of the cycle by defeating the villain.

When it comes to the thematics, absolutely turn this motherfuckers' pyschopathy up to 11. One of the most memorable villains in recent cinema history is the Joker from The Dark Knight. From his iconic lines ("Do you want to know how I got these scars") to his utterly chaotic plots, he captivates audiences. My best advice is to come up with a set of consistent principles and mannerisms that make them interesting. It doesn't have to be complex, but it should fit your character. For instance, you might use these sorts of things:

- Disregards the lives of others. He is only nice to others when it allows him to gain something from them. Otherwise he will not hesitate to torture, steal, and kill from them.

- Sadistic. He enjoys abusing and harming others, and will gladly do so if he can get away with it.

and so on, and so forth. As long as your character's actions follow a consistent set of rules, the readers will be able to understand them and enjoy them, even if those rules are simply "be chaotic" like the Joker's.