The build quality on all of Northwest's products is very good. They are not flawless, but they are well above average, and very wiling to stand behind their product in the case of any blemish (I've only ever seen cosmetic blemishes in the gel-coat). The rudder system (always the weak link in kayaks, it seems) is constantly beingin improved, and is as basic/durable as any I know. It isn't pretty, but it works well. Our organization had seascapes that were over 8 years old and going strong. These boats were used at least 50days/year, mostly by teenagers, and were transported by all manner of trailers, powerboats, and towing. They are, indeed very durable and easily repairable.
The design of the Seascape is really quite remarkable. This boat is extrordinarily stable in rough water even with beginners. Several times I'd see people become sea-sick from the pitching and rolling in big seas, but not be nervous about the stability at all. I've seen a set of large (8') waves move under a fleet of Seascapes with no concern on the part of the paddlers (I, of course, was plenty concerned and was setting up rescues in my mind). Beyond its stability, the boat handles well, is easily steered by strokes, and is reasonably fast. It also holds considerable cargo, including large items that would never fit in a solo.
I rated this boat relative to other tandems I've paddled and relative to what I think it ought to do. It is not as fun as a shorter solo boat with some rocker, for instance. I do think it is one of the best boats for serious expedition paddling due to it's stability, speed, and capacity.