Where it offers a mechanical challenge, it's very easy for its level range - almost trivial. A single lesser demon to fight the entire party? Low-level fighters with no magical support? The supposed aspect of the god of feral savagery is an 8-HD monster, physically humongous yet pathetically weak? An embarrassment to divines everywhere.
Where it tries to string the party along its plot-beats, it at one point offers two options on where to go, yet only one of those options is objectively correct. The other one is a waste of time. The players have no idea which is which until they flip the coin. Otherwise, a lot of things happen where the players can have no input in, with no chance to change things. In a few cases the book doesn't take into account an obvious course of action - such as raising a friendly paladin from the dead. And of course there's a very important NPC who's needed for anything to work out fine.
Tony DiTerlizzi's famously imaginitive artwork earns a point of merit, as it always does. Some good imagery and interesting seeds of situations, Planescape's trademark planar philosophy and alignment struggles. But none of that makes for an adventure on its own. Themes and set-dressings - some carpets and drapes are on point, but the walls are rotten.