Oslo is nice albeit everything is very expensive. In fact the last time I was there I saw a keyring that said "This is the only thing I could afford in Oslo", which made me laugh. Not sure what time you dock and leave Oslo on your cruise but get up early and watch the scenery as you sail in and out. My goodness - it is so absolutely breathtaking and beautiful.
In Amsterdam just be warned that the smell of marijuana is everywhere. You can be walking down certain streets and behind certain people and get high just being around there for 60 seconds. If this could be a trigger then watch out (I never liked dope so it didn't bother me albeit I held my breath). If you're overnight in Amsterdam then have a meal out and take in the nightlife. It really is something else.
Enjoy your cruise. I'm jealous!