While not my favorite in the robot series, Robots and Empire was still thoroughly enjoyable. I liked that it was centered more directly on Daneel (and Giskard). Rather than using them solely as plot devices and supporting characters, they are now full-fledge completely hashed out main characters. It's also nice to learn more about Gladia without her becoming insufferable. 
4 stars because it was great and enjoyable while also informative.