There are hints of the cult of Bhaal and Gortash taking over all over acts 1 and 2. I just found a note in act 1 in the entry to the zent basement talking about Gortash. The goblins talk about their 3 leaders, and you quickly understand that they're not the goblin, the drow and the hobgoblin.

Ketheric was merely the first step, and saving the duke comes in act 3. There are many pathes to save him or not. Really that's not railroad that's happening, that's vilains having more in their bag that you'd hope for.

These are good vilains, and it is a good story. Far better than a story that doesn't move forward and has its vilains protected by scenarium.