I'm definitely still interested, I like Ivar (well, "like" may be the wrong word for the toddler axe murderer) and Bjorn, Ubbe hasn't done much yet but the actor seems pretty good. I've always liked the Wessex scenes more than the online consensus seems to be, the revenge invasion should be good.
I don't really care about Lagertha anymore though, she's just been treading water for seasons now I don't get much more out of her taking Kattegat than gaining and losing control of wherever she was Earl multiple times. Though confrontation with the rest of Ragnars sons about Aslaug could be good. And I'm curious when they will reveal her fountain of youth so that she looks to have aged a few years while Ragnar was aging 25-30(/s).
Anyway as for Ragnar himself, I thought the last few episodes for his end were handled pretty well... but I do wish we had gotten another season of prime/ambitious Ragnar in the series. He was either injured, addicted to drugs or with a death wish the the last 17 or 18 episodes and this is only season 4. And we got virtually no information on what he was doing during the time skip.