Harder than I thought!
I figured given my levels in Swedish and Danish that Norwegian would be a breeze. I was all ready to assume that boy was "dreng" and was not prepared for the existence of "ei" as an article. I underestimated the degree to which Norwegian has its own identity!
I'd say learning how to distinguish things between really close languages might be more difficult than learning languages that are more loosely-related. The distinctions are strong enough for it to have its own identity, but the similarities give you a sense of overconfidence that can prove you wrong time and time again.
Good luck on the continuation of Nordic adventure!