Just got home from 7-day cruise on the Oosterdam. Wish I was still on the ship. I have only had one experience cruising and it was on the Carnival Holiday about 12 years ago. That was a much smaller and older ship. The Oosterdam was much, much better.
Transportation to Pier 91: We took link light rail from airport and transferred to bus for about $5 each. Bus dropped us off on a bridge and we had to climb down a number of stairs with all the baggage, which was a challenge, but we were not sorry because we got to see some of the streets of Seattle and bus driver and light rail employees were friendly.
On the return, we thought we would take taxi, but the organization of the taxi system at the pier was horrible. We finally decided to go with Shuttle Express back to the airport at $18 per person. We just went outside the ship terminal and they were very friendly. We originally thought we would go with taxi to the light rail, but there was a long line and taxis were picking up people that were way at the back of the line, as they just wanted to grab passengers and not wait on the line to do it in the order they arrived. Taxi to airport could be from $45 to beyond $60. The sign on the cabs say, "airport $32 from downtown", but Pier 90 is further away, so don't be fooled. Encountered two separate hostile taxi drivers and the way they were picking up people was not properly organized, unfair, and chaotic.