The new sieges look really cool. Some might say it takes away from the gameplay, that you can only attack from one side, but I bet sieges will be more epic than ever now.
This is a very very important change in the gameplay, as such I dont have a precise opinion about it as long as I dont see a dozen sieges and how its being handled by the ai/player.
All sieges will kinda ressemble a helm's deep/minas tirith siege then? I can imagine some positives and negatives:
+ easier to handle by the AI
+ defense will be easier even with just garrisons (garrisons are increased compared to Attila)
+ settlements will not always need an army sitting in there (especially since armies are limited now) to be properly protected and epicly important capitals will not fall to 1 stack
+ encourages "passive" sieges mechanics (real siege, surrender by encirclement and creation of siege engines)
- fiefs defended by garrisons + armies will be clusterfucks and almost impossible to win by tactics (if you can position a 10 men deep unit on every foot of the walls, what can you do but grind them?)
- some maps will make no sense (not all settlements are built in a gorge or surrounded by impassable terrain)
- if defense is easier it will not necessarily benefit the meta-game in terms of epicness, except if there is large incentive and room for more field battles (AI camping settlements could be the #1 boring shit of Warhammer)