We also were on the last sailing to Alaska on the Bliss and had a wonderful time on this beautiful ship! As others have stated, the two main shows are Havana and Jersey Boys, and both are free of charge. If you can only make it to one of the shows, I'd suggest Jersey Boys based on our experience and others we sailed with. I was very surprised at how many people left Havana during the show, and felt that while it was entertaining, I wouldn't see it again. We made reservations online prior to boarding, but did notice many open seats during the show. If you aren't able to reserve seating due to it showing full, you can always try the stand-by line (and my guess is that you will get in based on all the empty seats we saw).
We chose the 3 free specialty dining meals as one of our perks and did enjoy our meals at each. We had reservations for Cagney's twice and Le Bistro. While the meals were good for the most part, I wouldn't pay extra to eat there if I did not receive it as a perk. On our next sailing, we will try different specialty restaurants to see which ones we like best. Really enjoyed all of our meals in the MDRs...both Taste and Savor. We found after the first day that if we brought our first drink (soda) to the table with us and ordered another one right away, things went smoother and we were never waiting for a refill.
We hardly ever felt the ship was crowded at all except a few times trying to find a seat at the buffet and in the elevators after shows. We ended up finding tables outside on the pool deck and always found a seat there. The Local was also mobbed for football all day on Sunday, and we were happy that we could also watch the games in our stateroom if we wished. Many times we were surprised that no one was on the elevators and at other times they were somewhat crowded. We took the stairs going down whenever possible, so that did help.
We loved all of the staff we encountered and thought the ship was very clean. We were very sad to leave after a mere 7 day sailing, and kept saying on the last morning that 7 days is not enough for us. I'd suggest really exploring the ship on your first day, and find venues that fit what you are looking for. Hopefully, you will love your experience on the Bliss as much as we did!