How does one stop sushi seaweed wrapping being too chewy?
In addition to what Jason says above, which is absolutely correct, nori needs to be toasted to be crispy.  Sometimes you buy it ready-toasted, but sometimes it's not toasted and you need to toast it over an open flame yourself.  How to toast nori instructions and video.

Additionally, I've found that if you live somewhere high-humidity (like San Francisco, where I live), you sometimes need to re-toast nori even if you're buying ready-toasted packets, because it becomes moist.