I think in M2:TW, if you plan to take a huge Castle, you will need huge cannons. I think when you are trying to take the castle, you will have to think carefully about how you use your cannons. Blasting a hole in the first wall is all well and good, but you might have to knock down a few towers so your cannons can go through to the next wall unchallenged.

I look forward to Defending Castles in M2:TW. I pray to God that the AI in sieges is better in this game. The RTW AI would certainly never win a siege if they attacked a Castle from M2:TW. I hope to be able to defend Jerusalem with a Small army of Christian Knights and Archers from Thousand of Saracens. Hopefully I would be able to kill alot of them at the first wall before being overrun and retreating to the second wall and killing more and finally to the third wall, where my brave Christians fight to the death in defiance of fate. I would expect to use genius military tactic to do all that, not exploit faults in the siege AI.