Pulling on the Core High GTX boot after wearing standard clumpy leather things, is a bit like that trick where you weigh your legs down for several minutes, and subsequently they feel like they're floating away. They are significantly, noticeably, instantly light.
In part it's down to the GoreTex Surround membrane which adds an all round airiness, and is complemented by the Nano-Cells construction; "breathable cells that wrap the uppers and give structure to the shoe and promote elimination of humidity." That breathability is palpable in that your feet instantly feel unconstrained, and this adds greatly to the lightness of the boots.
Low weight often leads to a lack of support, and that compromise is unavoidable here. The soft, spongy sole unit has the strange effect of seeming to wrap around the sides of the foot, rather than just being a solid, flat platform. Great for comfort, and in fact for sensitivity on the trail, but not so great for stability. You wouldn't want to hike 30 miles with a heavy pack in the Core High GTXs, but then La Sportiva wouldn't recommend them for that purpose.
With that in mind, it's probably not the all-things-to-all-men hiking boot that many people will look for.
However for rapid short day hikes with minimal gear and in any weather - and for dealing with the extra moisture that moving fast will create - the Core High GTX is a fairly unique offering.