Just to chime in from early November experience.

I stayed at the Best Western Plus Oslo airport for two nights on points; a great use of points by the way. (And I find non USA BW properties to be decent - clean/comfortable rooms, decent breakfast buffet - in fact in this case, breakfast was excellent. Of course it is Norway and the $15 draft beer was eye opening.)

I did use the punctual shuttle, to/from hotel/airport, several times at a cost of $7/each way. I used the Vy train to go into the city twice - the first time, round trip, for ~$22; the 2nd time, included a full day pass - all modes of transportation, for just ~$5 more. I used the tram, the bus, and the public ferry. I purchased the tickets from the agent at the airport.

I think I still came out ahead vs. staying in the city at a cash rate.

I also highly recommend checking out the Barcode and the Mathallen food halls. Very unique and many choices at reasonable prices.

(The ticket agent inadvertently sold me the wrong ticket for my first trip. He actually came to find me, apologized, refunded my money, and issued a correct ticket. I thought that was very nice of him as the original ticket would have likely worked had I been asked to produce it, but it turns out it was twice the cost of what it should have been.)