Well apparently there's a link between the Sharingan and ones emotions. The Sharingan itself is awakened in response to sufficient physical and/or emotional stress. Furthermore, for it to progress to Mangekyou Sharingan requires that the user experience the traumatizing loss of someone precious. Even the Eternal Mangekyou Sharingan is obtained by transplanting the eyes of a close relative into one's self. The EMS takes the combined form of the two Mangekyou Sharingan; it is power granted unto one by their own family. The Shinto religion postulates that Gods and spirits reside in everything, so having EMS is like carrying around a piece of their soul with you. It's like they're watching over and protecting you.
Other than that, I know about the two main abilities of the Sharingan; insight and hypnosis. As the eye of insight, the Sharingan has the ability to see and distinguish between different kinds of chakra. For example, (I think) the Sharingan can differentiate between things like fire and water element chakra, as well as being able to see irregularities in a person's chakra flow (like someone caught in a Genjutsu). The eye of insight also grants one clarity of perception, offering them certain predictive capabilities. It can track fast speeds, and predict how someone will attack in close range by monitoring the minute bodily movements leading up to said attack. Additionally, as the eye of insight, the Sharingan endows the user with the ability to copy and memorize almost any jutsu assuming they are physically capable of performing it.
As the eye of hypnosis, the Sharingan allows one to utilize a unique brand of gripping Genjutsu that are known for bending a persons sense of reason and understanding (or something like that).
-------------
Sorry, I got a bit lazy at the end there. Is anything I said inaccurate? Is there anything I missed?
