As a fan of the series since Rome, it is easy to admit that there is no perfect Total War game, but it is a large irritant to see the series make the same damn mistakes and absolutely lie through their teeth about AI and gameplay improvements.
MTW2 was broken on release and had numerous bugs with unit stats, (shields would remove armor rating and double handed units could not attack cavalry) and still has broken AI that wasn't fixed.
Empire also had unresponsive AI that didn't know how to use ships for naval invasions. Also, one of the patches broke the battle AI which caused units to just charge, and every battle became large melees.
Napoleon and Shogun 2 were improvements, but the series also got more streamlined. Hopefully when they announce the new game this month they'll actually try to make a quality product again.