The sailing is pretty accurate as such, but I am not sure the vikings had the type of rigging that let you sail up against the wind. Noone is; there is no surviving rigging from the time so there is some guesswork. The boats were certainly fast in a tailwind; they have the speed pretty accurate with existing replicas and simulations.

And, when the wind fails, rowing is faster. Which is also accurate.

My GF did a lot of sailing as a kid, had her own sailboat, and says it feels right and that it's obvious the developers have done some sailing.

That's good enough for me. But it's not a simulation - anything which automates rigging and doesn't let you make mistakes is pretty far from a simulation.