Our first mobile review (I think), and it's about one of my favorite series.
Fallout Shelter (going forward simply known as FS) is a Simulator have where you build your own Vault. As the Overseer, you must make sure everyone is happy, and keep that's at bay. This sounds easy, but as you may know, that's never threw case.
FS is overall a very simple game to pick up, but it will require a sharp mind to master. Like many Sims, you have resources, FS is no different. You have Food, Electricity, Water, Stimpaks (restores health to dwellers), and RadWay (removes radiation from dwellers).
As your Vault grows, you'll need more of the first three, and depending on how well you maintain your Vault, and how often you send dwellers in to the Wastes, you may need the latter two.
Failure to properly maintain Food, Water, and Electricity results in dwellers getting radiation poisoning (hello Mole Rat meat and toilet water), or other posts of the Vault shutting down. So make sure you keep an eye on your reserves.
So, you may think, "Oh, I'll just build Food/Water/Electricity generators and be fine." You'd be wrong, mostly. Each dweller has their own stats in the S.P.E.C.I.A.L. (Strength, Perception, Endurance, Charisma, Intelligence, Agility, and Luck) system, if you're unfamiliar, just think of that as your basic stat system. Certain "buildings" require certain stats, for example, the Water Filtration systems require someone who has good Perception, the Kitchen requires Agility, etc. The higher the correlating stat, the better they perform.
"So", you ask, "Is that all you do, build a Vault?" To that I say nay. You also can send you dwellers to the Wastes to find gear and money (protip: a high Luck helps), equip your dweller with some armor and a weapon (or don't) and send them out. They will search the Wastes until you tell them to come back (protip 2: it takes them half the amount of tune to return, so if you have them out for an hour, it'll take 30 minutes to return).
Be careful, the Wastes are filled with dangers, on top of gear and money, your dweller can also earn EXP from killing the various inhabitants (which is why weapons and armor are suggested). As your dwellers level, they become stronger (protip 3: S.P.E.C.I.A.L. does not increase via leveling, just health).
Just in case you thought the Vault was a safe Haven, you will frequently be attacked by raiders, they generally go after your food storage first (at least in my game), so make sure you keep some dwellers armed.
As you gain more dwellers, either from other joining, or procreation (sex), you will gain more buildings, so check those out to see how many dwellers you need.
You are also given goals to achieve, these are small tasks that offer monetary or lunchboxes as rewards. The latter offers a handful of random items such as money, weapons, armor, or special dwellers (you can also buy them with real cash).
All in all, Fallout Shelter is a very interesting and fun way to waste time, and recommended for any fan of the series.