While the game is very difficult, it is not truly challenging in terms of strategy or tactics. This is because there is no time limit on your campaign. No matter how badly you play will never need to start over as you would in XCOM, and eventually given enough time put into the game you will acquire enough resources to upgrade all your buildings to the max. Which is basically required in order to progress at all.
So in reality the game is just incredibly grindy. Its not about making the right decisions and starting over if you make the wrong ones. It is only about investing enough time (ALOT!), until you acquire enough resources to be able to beat the game. Which is not a rewarding form of difficulty.
Despite all my complaints the game is probably worth the low cost simply for the fun initial experience. As mentioned the setting/art/narration is great, so I suppose I would still recommend the game even tho it was pretty dam disappointing in the end.