.
Deus Ex is one of my favorite games but it sure as shit is not a masterpiece if going by the definition that a masterpiece is an as-close-as-possible-to-perfect work. Game is riddled with problems, specifically being far too easy given the amount of options you are given, enemy AI is braindead, which allows stealth to be too easily abused, it was a pretty bad looking game even at release, level design could be inconsistent, and so on. Thief: The Dark Project and Prey 2017 are near to masterpieces of that genre, but both of them have issues as well, especially Prey with, again, being too easy given the amount of options the player is given (common theme with this sub-genre).
.