EDIT: To be more in depth, the game is fun but difficult.
The whole thing is a careful balance between Power, Food, and Water. Rooms run on Power generated by power rooms, and vault dwellers run on Water from water treatment rooms, and Food from the diners. Each Dweller has a full set of SPECIAL stats, which help you determine where they work best. Agility works best in Food rooms, Strength works best in Power rooms, and Perception works best in Water rooms. Then there are living quarters, which determine how many Dwellers you can have, and allow you to make Dwellers by reproduction (yes, it's even comical and true Fallout-style). You need to keep your Dwellers happy, otherwise they won't work effectively. My first Vault succumbed to Raiders and Power shortages, leading to blackouts in Water Treatment. It was a mess. Entire families died.
The big thing about the game is that you need no internet connection to play, there are no advertisements, and there are no payout walls. It's completely free. The only thing is in-app purchases to buy Lunchboxes, which are like booster packs that contain random stuff you need like Caps, Resources, Weapons, Supplies, and even Dwellers and Outfits.
All-in-all, I give the game a very solid 9/10, as it is sometimes buggy. Oh, and it's only on iOS right now (I have a 5c)
Awesome, guess I'll have to get it then, I couldn't tell all that from the App Store review. I'm glad it needs no internet which means no multiplayer right? Cuz then there'd be an insane amount of vaults