The Norwegian coast in fall/winter can be marvellous, but the weather is unpredictable. Remember: these are working ships carrying cargo, and they need to stick to their published timetable. Although most of the revenue is made on cruise passengers, these are not cruise ships as such. The food is good, there are plenty of shore excursions but the entertainment is not of the Caribbean cruises type! It is much cheaper to travel in fall/winter: for å reason. But unless you know that you are not very susceptible to seasickness, your honeymoon could be very memorable for all the wrong reasons.

As for the western coast up to Ålesund being very cold in September, this is not really the case. To find permafrost in southern Norway you have to go high up in the mountains, which are quite bare in any case. The temperature in September usually hovers between 15 and 20 degrees Centigrade. Due to the Gulf Stream western Norway is actually quite temperate. Think Pacific Northwest, not western Alaska!