Round trip Seattle sailings are the least scenic and have the roughest potential. Expect it.
Tracy Arm is not a given for glacier viewing. Probably only about 25%+ of the cruiseships make the full transit for glacier viewing, which is at the end of 30 miles in. Some lines are diverting more to Endicott Arm for glacier viewing of Dawes, but, my opinion only, on the "glacier scale" neither of these has the forte of glacier viewing. The transit of Tracy Arm is very very nice, Endicott- so so. Again, only my jaded opinion, having sailed all the glacier areas. Mendenhall, is OK, again, not real exciting and rare to see calving. But excellent for an easy access and nice hiking, good visitor center, and cheap.