This product gives something that is sorely needed to give players a different kind of challenge as you give them monster encounters - skill challenges, of course! It gives a healthy plethora of great non-combat encounters (though there still is a few, don't worry!) to make your players go, "Wow, that was tough, good thing I had my stone shape, or else we may have suffocated there."
It really gives other players who aren't so combat focused time to shine, and even some of the combat focused players a way to help those players out.
A must-have for any DM who may want something more than just, "Sword guy hits Spell guy for XX damage."
Bonus: It even has some other content about difficult terrains and complex traps too, so he's got you covered for when things don't go quite as planned and they accidently steam-rolled the challenge.