The story seems interesting. Nothing too spectacular so far, but I don't think that's a bad thing. Fits the authentic/historical theme of the game and provides enough of a plot to keep you going.
The first mission was nice, a bit easy and short, but I guess that's to be expected from a first mission.
I like the roleplay elements (if you can call them that), always been the thing I found most fascinating about the Cossacks campaigns. I hope future missions will be larger/longer though.
The visual design was really good as far as I can tell (didn't explore more of the map than necessary), liked what you did with the city/port area.
Overall a pretty good preview, makes me look forward to the finished campaign.