Like @Pea666 , I'm unfamiliar with the boardgame but from what i see and read in the rulebook, it seems very fun.
I am a bit confused about game-ending scenarios because I did read that a set of cards determines the objective (for each player?), to increase the replayability. But it also states that you can win either by destroying the entire fleet or by having the highest score (hostile ships destroyed) after six rounds with no victor. If it is the case, that you have objectives but you can also win by having more points after six rounds, I'd just get rid of the "win after sox rounds with highest points" clause. If there are no set objectives, I would sit down with your son and come up with interesting and fun objectives that, upon completion, declare the winner instead of this "technically you can win by killing one ship and running away for five more turns", because that does sound like a boring base rule.