Of the Total War series, I've played Shogun 2 and Empire. Of those three, this is the weakest installment.
It is a clone of Empire with some changes. Those changes don't affect the core gameplay. I would be fine with the game if was essentially an expansion pack, but there are so many glitches, some which can cost you a battle. Let me name a few:
-units will stop responding. In one instance, I had an enemy cavalry regiment bearing down on an artillery group. I ordered the artillery to fire stop firing at enemy infantry and target the cavalry. The artillery stopped firing. They weren't reloading, they weren't doing anything, they just stopped. This happens so often with horse artillery (the really fast artillery pieces) I don't even use them.
-Units will sometimes do the opposite of what I tell them. On a number of occasions, I ordered an infantry regiment to charge an enemy. The regiment was at full strength, yet it started running the opposite direction for no reason. I kept ordering it to attack the enemy but this did nothing. The regiment had not broken or shattered, it just ran away for no reason.
-ordering grenadiers to throw grenades rarely works
-a wall was about to be destroyed on my fort so I ordered my regiment to the center of the fort. While it was in the middle of the fort, everyone in that regiment dropped dead the second the wall was destroyed even though they were no where near the wall. This frequently happens.
If you can look past the glitches, you'll like the game.