Prince of Persia was the best game in the genre in 1990, and it is very good now,too.
What is the Unique Selling Point of the Prince of Persia? It is the storyline, and how the various characters in the game aid the story of the game. The game is seamlessly integrated into it's story, and one cannot differentiate one form the other. In the original Prince of Persia, there were many Viziers with varying degrees of combat capabilities. The rule was, the fatter the Vizier, the more capable he was. I am glad that the current game has only one Vizier. I am still infatuated with the original Prince of Persia, so much so, that perhaps, all the sequels will be second best. I would rather finish the original, now, than the Sands of Time, which I purchased just yesterday.
The greatest Unique Selling Product of the game is how cinematic the experience of playing Prince of Persia is. One just does not know what to expect. I guess, the game is going to have Vizier(s) for villans until the game ends it's lifespan, which is a long time away. Perhaps, the developers of Prince of Persia, can think of a new adversary for the Prince in the next installment.