Focus on assassin training and easiness.
Easiness: Is the game easy to beat? If your goal is to win as quickly as possible just to see the stories, then it is. However, each task have 2 ways of completing...50% synchronization and 100%. 50% is accomplished by simply finishing the stated goal at the beginning of a mission (i.e. kill a guard looking for a citizen). 100% is only accomplished if you follow a second guideline shown at the start of a mission (i.e. kill the guard without killing anyone else). If you are trying to accomplish tasks with 100% synchronization, then it becomes quite difficult. For example, if you cannot kill anyone except your target to reach 100%, this can be challenging if he is on horseback and surrounded by 10 other guards. If you then try to complete everything in the game, it starts to feel almost impossible to do every task possible with 100% synchronization. So, if you feel the game is too easy, then perhaps you should try to complete every mission at 100%.
Assassin Training: Some have said this is pointless, but I find it extremely useful. Of course extra help isn't a requirement to win most battles...even 20-on-1 battles...but in order to complete tasks at 100% synchronization, it often helps to smartly use your trained assassins. Also, their contracts sometimes have rewards that include items needed for the shop quests. I agree that it would have been nice to have more of a significance to training once the end is reached, but it is still a worthwhile addition.
Overall: I think this is an excellent game. Very comprehensive with tons of missions. Most missions are optional, but they are valuable in gathering wealth to purchase items, so you will do many of them. The story is a little bland compared to the two previous games, but it oddly lends itself to the game for myself. What I mean by that is that the gameplay isn't intruded by the story to the extent where it's disruptive.