Normally, Genjutsu Sharingan is only capable of things like hypnosis and illusions, and a myriad of other powers, getting stronger and stronger as the Sharingan upgrades. However, no matter how strong it gets, it cannot control the concept of "time". Tsukuyomi controls not a person's concept only "space", like the Genjutsu Sharingan does, but also "time". This means that not only can Tsukuyomi causes illusions of any sort, but also control the victims very concept of time in how it is experienced. A three second illusion turns into a three days long torture session.