I personally find sieges boring, mostly because I'm on the receiving end and the ai is HORRID. Bastards sometimes just stand there when they control the gates and their catapults have crushed the entire wooden wall and wooden towers. So once I sent my general to bait them in, the first time it didn't work so I charged again and a ball from a catapult miraculously smashed into my general.
So I retreated the horses and I was quite out numbered, but the enemy didn't move. So I took the remaining cavalry and out another gate and flanked the catapults and charged them and watched as one was destroyed by another catapult lol. After taking them out I charged at the men on the outside of the wall, I hit them hard and then pulled back 100 yards, and to my amazement I had killed nearly 100 people just in a split second charge and only lose 3 of my horses. So I kept repeating untill my bodyguard was dead and they ended up killing about 600 men just by charging (this was a force of 20 horses).
So after they all died I sent my infantry in who were at the square and they slightly outnumbered the now battered opponent, but they folded and I lost Metz.
What I prefer are open field battles, with the varied terrain there are unlimited tactical possibilites.