Same female lead. Both are brilliant sci-fi dramas, and both feature brilliant mind-blowing plot twists. Both feature a main character who isn't human having to adjust to a human environment (an android in Are You Human Too and an alien in Circle). Both must-watch dramas. Circle is heavily underrated though.

Both stories are exciting revenge tales. But they're also quite different.

Both series are thrilling revenge stories staring Kim Nam Gil. If you like one you will undoubtedly like the other. ^.^