This is an engaging game that definitely tests your skills however it has a serious flaw they need to patch in an update.
It concerns your first minefield.
If you detonate one, it messes up the mission causing that territory to not be able to get down to threat 0.
This in turn prevents the final upgrade to your harpoon which effects your ability to bring down things requiring the final upgrade.
I'm sure there's more it effects in a domino fashion, I haven't gotten that far.
If you're the type who likes to finish a game, don't buy this unless they patch it.
I wish I had known.