Every villain is shit and is portrayed as some kind of psycho that must be stopped asap and the MC ... is bound by overly strict guild regulations. The bad guy have
to come to him. That's frustrating and really hard to watch. What kind of breed of masochists does the author believe his readers to be? The more evil the villains and the more evil deeds they did, the more rewarding their defeat? Is that what the author believes? That's wrong. At some point the rewarding pleasure of seeing one asshat finally being removed can't be increased anymore by adding more evil shit he/she is doing, no matter who many peoples lives he/she ended/destroyed. There is this limit and as an author there is no need to go beyond.
They introduced those three psychopaths, who love their atrocities. Okay. And now get rid of them all quickly. If their end is swift, their appearance might be forgiven by those, who continue to read this.
@xboxbam: What BOTMAN wrote would indeed make better villains than those here. I can also agree on your "evil, but has a well written BG-story"-villain approach. Those guy here have been portrayed as being different kind of scummy evil. Well, at least everyone seems to be a plain copy of a
different type of generic scummy villain. The braty murder hobo, the psychopathic freak and the self-loving "I'm the hero so lick my boots"-bastard. And most of them are rapists. Still they have been introduced in such a shallow way and already have been de-humanized or demonized by their deeds (standing around and having a good time while watching somebody getting raped is also evil), it's hard to believe the audience is willing to take any further deepening of their characters. As the are right now they are only useful as fuel for a revenge-type MC and as such there is no need to keep them around as they are an irritant that let's the fun-factor of this manga decrease.
To answer you initial question: My take on an interesting villain would be to let him/her surprise the readers and/or make at least something about him relatable. If he/she would have been wronged in the past in a way the readers can feel sympathy with him/her, that's relatable. If you make him a power greedy bastard, well everyone is power hungry more or less. Show that a portion of his ambition is close to something the readers also felt at some point (maybe while playing a videogame about galactic conquest). Maybe he/she wants to be finally recognized and actually deserves to be in a twisted way, because his/her has been injustly ignored/overstepped (cry for revenge) or his/her deeds just have been outrageous, clever, mindblowing, unexpected in their outcome, funny? or recognizable in any other form, so that the reader has to say, "Hey! Give that guy/gal credit." Doing something unexpected is also something good to make a character interesting. Letting a villain slaughter a village is boring, letting that character slaughter a village the reader expected to be around for longer is better. But if a villain, that has been mildly evil and been known for being relatively quite, peaceful and reasonable, steps over the corpses of known and beloved townsfolk and the head of that nice uncle Joe, people who he/she seemingly had been on good terms on before, and mutter something like, "That'll do for now.", that is even better. Surprising the audience of readers is always a good way to create a good villain.