Not the best, but pretty good
One of the features that interested me was the new Papacy features for the Catholic factions. The College of Cardinals was an interesting addition, and helped to gain favor with the Pope, another new feature. But perhaps the most interesting thing of all was the Crusading system, in which you lost favor if you did not join the Crusades. However, Crusading armies lose units due to desertion, and this can happen rapidly sometimes even if you are heading towards your target, which can be annoying.
All in all, good game, not the greatest of the series though.