The Mosquito Coast is a movie that has many things going for it, but fails to combine all its excellent ingredients in a way that makes it feel great. I think there's still a good deal to like, but overall, it feels a bit unsatisfying and disappointing.
You have an interesting premise, with a deranged father leading his family to live in the wilderness. You have Harrison Ford playing one of the most villainous characters he's ever played (maybe the most villainous?) You have a great supporting cast with people like Helen Mirren and River Phoenix. You've got a fantastic composer in Maurice Jarre. And then there's Peter Weird directing, who's made several classics, often involving themes of isolation or "adventures" that go wrong or people getting by in unfamiliar situations.
At the end... it's fine? It never really hits that point where it becomes something else, though. Maybe it's Ford's character- while I found it a breath of fresh air for the protagonist to have few, if any, redeeming qualities, maybe that hurt my engagement with the film in the long run.
Anyway, good premise, good acting, good music, and the the way it's shot is solid, too. Maybe it just needed a tighter script to keep things more interesting, or at least more consistent. It does feel poorly adapted into a movie, screenplay-wise. You can tell these lines are from a novel, with much of the dialogue sounding like they're just reading off a page.