- parts of the AP are railroady, for example, a trek through a fire forest in which walking outside the path is impossible because the forest is on fire, and going back is impossible because flames close the path as the PCs move forward. So the PCs can only walk along the path and go through the encounters the DM throws at them. Or, another example, is that an NPC tags along with the PCs from the start of the AP and leads them from encounter to encounter for some time.
- In the 4E version, it is my impression that the creature design and encounter design are suboptimal. Not as in, too easy. But rather, they're not as balanced or rules-aligned as they should be.

- parts of the AP are railroady, for example, a trek through a fire forest in which walking outside the path is impossible because the forest is on fire, and going back is impossible because flames close the path as the PCs move forward. So the PCs can only walk along the path and go through the encounters the DM throws at them.
At a 4 hour session once per month, it took almost 3 months to get from the start of the module to the point in the Fire Forest where the meaningful choices come up. {at the village}
The second thing to point out, my players recall the straight jacket of the road much clearer than they recall the choices or the insanity that is the capstone battlefield, mostly because they had selected an alliance and were not aware that the options were fleshed out for alternate endings.
I can see why the first two partsd of WotBS might seem railroady from time to time, but that may be deceiving. I recently bought and started reading "Death Frost Doom" and found one of the author's comments quite interesting: He's describing a trail leading up a hill and mentions that if the party follows it, they won't run into any trouble while strying from the trail will result in a difficult journey. He then points out that this is not 'railroading', it's the very definition of a trail. If it wasn't easier to travel on the trail it wouldn't be a trail!- parts of the AP are railroady, for example, a trek through a fire forest in which walking outside the path is impossible because the forest is on fire, and going back is impossible because flames close the path as the PCs move forward.
Now, this surprises me a bit. Which parts do you feel are railroady? I should think it cannot be the dungeons, since they twist and branch all over the place. It also cannot be the city itself, since the pcs are free to go wherever they like.The Shackled City had too much dungeon crawl and was very railroady (perhaps even more that WotBS)

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.