Nat, Alaska cruises sail three different itineraries: a round trip from Vancouver or Seattle, a northbound cruise from Vancouver to the Anchorage area, or a southbound cruise from the Anchorage area to Vancouver.
The northbound and southbound cruises are great for those also doing an inland tour to places like Denali Park and Mt. McKinley, either before or after their cruise. The round trip cruises are great for folks not doing an inland tour.
Most cruises will stop at some combination of Juneau, Skagway, Ketchikan, and/or Sitka, and will sail past glaciers. Any or all of those stops are terrific with lots to recommend them.