Actually I've just played one damn long campaign and what I can say is that performance and stability wise its great, but the AI leaves a lot to be desired and the game has some fundamental design flaws.
Ok first some bugs I encountered, there's one where when unit comes as a reinforcement and enters the battlefield it doesn't pass the battlefield border completely,some soldiers remaining behind the red line., I lost a few battles this way because I couldn't kill that unit, and had to retreat.Another would be that the game slows down like hell on the world map where there is big cluster of enemy armies around, and you'll see that a lot.
The AI even on the hard difficulty can be really retarded, If I create one solid line of infantry the enemy just comes in small waves which are annihilated by my line. This happens in 90% of the battles. Also on the world map the enemy cant attack a nation if its attacking through its ally's borders, the armies just bunch up there doing nothing.
One fundamental design flaw is the new reinforcement system where there can only be 20 units for each side at any one time, thus you can fight with one army against 6 no problem, cuz they cant surround you or anything, they are can never outnumber you another flaw related to this is that all the reinforcements come through one point(for one army), thus you can pretty much group your units at the border and create a cross fire formation, the enemy units come one by one and get slaughtered, whats worse is that sometimes your ally reinforcements come though the exact same place as the enemy and sometimes behind the enemy's line thus getting slaughtered in the process.
Another flaw is that when defending a city there is no incentive what so ever to defend the walls, you can only kill of about 10% of the enemy tops and once they climb the wall the melee battles take a huge toll on your troops and the outcome is uncertain, its much better to defend the town square and create crossfire fields and since the enemy again comes in small waves they are completely wiped out. Although this isn't as flawed as in Rome total war where your units were rout proof when inside the town square( the best system is in Medieval 2). Another complaint would be that I only had to ever use the basic line infantry. Anything like light infantry, cavalry and artillery where pretty much useless and nothing but a a hassle(although the very latter artillery is pretty good) and the only time I ever had problems in battle was when the enemy had more line infantry than usual. Basically light infantry is too weak, cavalry is useless once the square formation is developed and artillery will only ever take out 5% of an army at its very best.
While the game makes a lot of progress in some fields including AI, it's nowhere near as good and balanced As Medieval 2, great game but not as good as its predecessor. I haven't tried the toughest difficulty yet since I don't wanna lose another 2 weeks of my life since this game is pretty addictive but only fun for the first few hours.
Essay Pro