Re: Kishimoto the Great fails.....
Yes Tsukuyomi is unbreakable by most. (Excluding the Jinchuuriki)
Yes it is the strongest form of Genjutsu.
Yes it is strictly a Mangekyō Sharingan technique.
and Yes you need BOTH Amatarasu&Tsukuyomi to use Susanoo so therefore Itachi, Madara AND Sasuke all have Tsukuyomi
However, Itachi stated that Tsukuyomi can only be broken by a Sharingan user that shares the same blood as him; as demonstrated when Sasuke overcame Itachi's Tsukuyomi in their battle.
-Susanoo, also known as the Tempestuous God of Valour (勇武の荒神, Yūbu no Aragami), is the third ability granted by the Mangekyō Sharingan to those who awaken the abilities: Tsukuyomi — which symbolises the "darkness of the spiritual world" and Amaterasu — which denotes the "light of the material world"
-Sasuke can also perform Tsukuyomi with his right eye, though his illusion is considered inferior to Itachi's Tsukuyomi since it does not alter the opponent's perception of time indicating he has yet to master it.
Now that we know that Three ninja (Itachi, Sasuke, and Madara) have aquired Susanno at some point they are all assumed to have Tsukuyomi!
However, Tsukuyomi is by no means flawed.
-First, the Jinchuuriki are able to break its hold as demonstrated by Killer Bee in his fight against Sasuke.
-Second, anyone of the same blood (i.e. Uchiha) can break its hold even with a 3 Tome Sharingan as its how the Ninja use their tools¬ how powerful that tool is.
-Third, its been proven that you can complete avoid Tsukuyomi by simply not looking into the Mangekyō Sharingan as proven by Kakashi&Gai. (with proficient users like Itachi having the ability to use it with simply his finger.)
-Fourth, Not every Uchiha will awaken their Mangekyō Sharingan.
-& Fifth, Using Tsukuyomi uses incredible amounts of chakra and causes strain on the Mangekyō Sharingan causing the users eyesight to deteriorate. This is a MAJOR weakness in the Mangekyō Sharingan. Eventually the user will be unable to even use the technique any further unless they have recieved their Eternal Mangekyō Sharingan (which in itself is a feat to be conqured.)