Medieval 2: Total FRUSTRATION
Siege warfare is much more challenging than with Rome TW. The computer AI does a pretty good job.
BUT, you won't be battling rival factions in the campaign as much as you'll be fighting back rebel armies that were once yours. Send an army out of a town or castle without a general, and there's a very good chance that you'll soon be spending many more turns raising an army to defeat what you spent many turns creating.
The crusades are a joke. Trying to navigate an army to the crusade target through the web of cities and castles, hidden by the fog-of-war, will cost you a unit every time something appears in your way. It's just a waste of 9 units and a general. Crusading computer AI armies don't suffer the same fate. While at war with France, the computer camped a large crusading French army between two of my cities. Attacking this army would cause my faction to be excommunicated by the Pope, who just happened to be from my faction.
Money is tight in this game, and even with taxes at their maximum, you won't be able to stop the rapid influx of people into your cities. It's not long before city population out paces your ability to buy the upgrades needed to keep your population healthy and happy. In a state of unhappiness, all it takes is the infiltration of a foreign spy, or a siege laied by a one unit foreign army to send your city into rebellion and total loss.
I played the living hell out of Rome: Total War, but cannot get more than 70 turns into Medieval 2: Total War before I've just had enough of the constant bs. For me, Rome: Total War is going back on my PC, and Medieval 2: Total War is going on eBay. It's just not entertaining.