DS9 had some fantastically acted characters in the alien department: Garak, Dukat, Weyoun, Kai Winn (the fact she was so irritating was because of her acting), the female changeling, Gowron, every Ferengi, even bit parts like Damar had actors that gave the character distinct personalities. The Jem Hadar without even names gave great performances. The funny part is the human cast seemed to struggle to have personalities. Other than Miles & Bashir, they just weren't very interesting.