Going through your questions.
Fun, yes. The turn based loop kept me playing longer than I planned to, and the art, sound and storytelling are the strongest parts of the whole thing. Main menu animations included, everything visual here is on point.
Most appealing card was the multi projectile one, but I should be honest about why. I took it every time because when my aim is off at least one shot still lands. Which makes single projectile the one that felt pointless to me, not because it is weak but because it asks for precision I could not manage. So that pick stopped being a real decision quite early. Maybe easier aiming, or make the single shot hit hard enough to be worth the gamble.
On difficulty, the aiming is where it is hard. The tactical side felt readable to me, I usually knew what I wanted to do, I just could not reliably do it.
Story got me from the first encounter. Every enemy turns up with its own reason for being there, so there is a point to beating them beyond winning the fight, and that is what kept me reading.
I did not finish. Two missions in and I had to stop, mostly because I opened it very late at night intending to glance at it for five minutes before sleeping and it did not let me. Coming back to it properly.
Replayable, yes. Swapping cards between battles is the reason. Being able to mix them across the different ships means the next run can look different, and I want to see how far that goes.