I’v not ridden the Giant but I own a GTC Agree.
I’d been riding a Focus Cayo for a couple of years and when I was working at a Cube delear, a customer was having trouble with the GTC Agree. I took it out for a test ride and was blown away by how much more comfortable it was compared to my Cayo. I was hoping that I’d managed to get an Agree cheap from the distributor, but as they’d basically all sold, I was stuck.
When the new years stock became available, I just bought one anyway. I’ve never heard a bad word about them and they’ve apparently improved them for 2012. Your most difficult task might be finding one!
I’d say that they are not the most “direct” in terms of race performance, they are squarely aimed at the slightly longer-distance rider (Sportives, that sort of thing). No problems sitting on one for 120+ mile days.