Sardis was a great change of pace from the tourist-filled Ephesus and Pamukkale. The gymnasium alone is very impressive, and has a somewhat different visual weight to it from the other ancient sites in the region -- more red brick than white marble, for instance -- and it's much less crowded. The synagogue is the largest known synagogue from the ancient world. The mosaics throughout the WHS are also nice. A pet peeve of mine is ruins without any signage, but Sardis doesn't disappoint in this matter either; there is plenty of signage in Turkish & English to explain what you are seeing with out it being overbearing. 

In terms of the negatives, the "museum" on site is very small and had actual spiderwebs across it when I attempted to enter. Some of the artifacts and mosaics are replicas, with the originals being hosted in various museums. Bintepe, the other component, can't really be entered but you can see it from the highway when you are driving to Izmir (at least I think I saw it!). The only part of Sardis I didn't see was the Temple of Artemis. As the former capital of the Lydian Empire, it was an interesting sight to see, and I would recommend to travelers already in the area :)