In the current issue of Thirteen1, an awesome online games magazine, is a 3 pages long review of Grappling Hook! Overall rating is 92%!
Some quotes from the review:

Grappling Hook is a triumph of design, requiring you to zip around at ultra-fast speeds through levels of steadily increasing difficulty.
It’s challenging, exhilarating and, quite simply, a joyous dose of reflex gameplay!
Grappling Hook is a must-play for all ‘Portal’ fans out there.
[…] once you try Grappling Hook, you will understand the sheer awesomeness it holds under it’s many blocks and turrets.

Grappling Hook is also part of the Thirteen1 – Massive Christmas Giveaway“!
You can win Grappling Hook, Aion, CitesXL, Trine, Fallout 3, We Sing, Section 8, Tropico Reloaded, Sins of Solar Empire, Ceville, F1 2009, a bunch of gaming hardware and even more. Just answer a few questions and hope that the luck is on your side.