The wardrobe design is pretty bad, at least for the Jedi. Despite the alien Jedi's facial features, overall, the Jedi come across as visually bland, all wearing brown hooded cloaks. I understand that Lucas was trying to stress the idea, visually, of Jedi living and thinking like monks but regardless the end result was making these characters look bland.

Kamino was a great looking planet. I know that's a theme of the Star Wars universe to have planets that are based on simple ideas: a cloud planet, swamp planet, desert planet, etc. So one fully covered with ocean continued in that same vein but provided some great atmosphere. Unfortunately the cloning station looked to "present day" in that it looked like the Apple store.

Purple should never been introduced into the Jedi's lightsabers. Blue vs Red, serenity vs anger was a simple but effective visual distinction for the good guys and bad guys. Luke was originally going to have a blue lightsaber in Return of the Jedi but for design resigns they wanted it to match the green of Endor. I'm okay with that because you could argue that since Luke was new to the ways of the Jedi, the lightsaber he constructed on his own, without proper training, might be different from the standard Jedi lightsaber. But having all the Jedi with blue, green, and purple lightsabers made it look like a rave, especially when congregated to fight on the wannabe Tatooine planet.

The droid cannon fodder had silly designs that made them look totally un-menacing.

I did however like the design and colors of the senate room where Yoda and Sidious do battle. It felt like Star Wars right there despite my gripe with showing Yoda bounce around like a pin ball with a lightsaber.