Now this is a nifty book. I've been meaning to make terrains a lot more prominent in my games and this book brings that in spades. Not only does it have some fantastic rules for how to make terrains into some wonderful challenges for my players, but it has brought to life an imagination full of new things I can do to challenge them.
The only issue I have with it are that some of the terrain obstacles are given a "to hit" for a player where the feel of it should really be based on a saving throw from the player. For example, one terrain obstacle has shattered glass all over the floor which acts like caltrops. This should be a reflex save on a part of the player to avoid the shattered glass, but instead they gave the glass an attack roll to hit the player. It just doesn't feel right. But don't let little things like that stop you from reading this - I am really enjoying it and making good use of it in my campaigns.
[4 of 5 Stars!]