Which game is worth it?

[Yuhaney]

Overture, 'cause of the storyline. If you start with Black Plague, Overture won't be so interesting to play 'cause you know almost everything that happened to Phillip on it.

And like Kedjane said:

You'll find trouble understanding on what's going on.
So, get Overture first! :

Buy the rest of them when you have more money.
Trust me, it's better that way.