King of the Storval Stairs presents a very simple scenario, the most straightforward of concepts. It's a slugfest in a pure form.
The fights are pretty epic, but it suffers greatly from having four of them, and from having too many monsters who are both hard to kill and cannot effectively damage the party. Thus, the whole thing became a huge timesink, my runtime lasting a total of seven hours.
Also, I noticed that the scenario really went out of its way to make the "tough" fight easier for the players to handle,
This assistance drops the CR of the big fight by more than the numbers would suggest. Giving 7-11 PCs that much assistance and that much prep time and that much terrain advantage is overkill.
I also noticed that the scenario tries to be really tough, yet goes out of its way to pull punches, with subpar feat, terrain, and spell selections on the monsters. It even goes so far as to hand the PCs an easy surprise round at one point!
In all, Storval Stairs tries to be a pure-form slugfest, but suffers from too many pulled punches, under-capable-yet-hard-to-kill monsters, and too much generosity. This combination leads to a grindfest which takes way too long to go through.
-Matt