One of the most economical lenses of the EF-L series, the 17-40 is particularly well suited for landscape photography. It's size/build/cost ratio gives it, in my view, an unbeatable value if you're looking for a quality replacement for the kit lens (18-55).
Although it may not be fast enough for some in low-light handheld situations, a flashgun solves the issue relatively well. A bit short if intended for owners of full frame cameras as a walkaround lens, users of 1.6 crop cameras may find the range more usable for that purpose. Also, 1.6 users don't have much to worry about in the way of vignetting.
Those who are undecided about this lens over the 16-35, luminous landscape has a fair comparative review of the two.
In any case, an excellent piece of glass all round. Highly recommended.