Like the Prequels themselves, he really was a missed opportunity.
The side prequel villains on paper and design are all really, really cool. Darth Maul, Count Dooku, Jango Fett, General Grievous all had potential to be more if the focus was on them. They could have rivaled Vader and Tarkin if they were depicted better. Having 4 different villains within the trilogy in addition to Palpatine and Anakin is just too much.
I like the concept of a mysterious Sith assassin that’s tracking the Queen. I like the idea of a bounty hunter that is so narcissistic he has a clone son that he raises as his own. I think the idea of a wise Jedi Master who abandoned the order and rebels as this anti-Ben Kenobi foil is fantastic. A cyborg general that is the leader of the robot army that hunts and kills Jedi and takes their lightsabers as trophies? That’s brilliant. They’re all great designs and concepts but I think it was wrong to feature them all. They’re all disposed of so quickly and they’re all under utilized. I know the point was that they’d be expanded upon in cartoons, books and comics as supplemental material for the movies, but they’re just wasted potential in my eyes. They should have taken Maul, Jango, Dooku and Grievous and narrowed them down to one villain. Just combine traits of Maul, Dooku and Grievous as one guy and have Jango be his go to henchmen or something. I don’t know. Attack of the Clones is the biggest offender though. Not only do you have Sidious > Dooku > Jango but then you have that shape shifting bounty hunter chick as an underling to Jango and the mysterious Jedi that ordered the clones and never revealed or mentioned again. Why? That whole movie has too much.
Still way better side antagonists than Hux, Phasma and Snoke though. I can wait to see how they use Captain Phasma again!