Announced and launched at Bethesda's first ever E3 press conference Fallout Shelter is a charming vault simulator that puts you in the role of overseer as you try to balance the needs of the dwellers (food and clean water), with security and power needs (needed to run various rooms in your shelter). It's a fairly simple yet surprisingly deep concept where you'll spend plenty of time trying to optimise your room placement, send high level dwellers on exploration runs to the wasteland to bring in resources (caps) and gear (weapons and suits).
At a glance the key gameplay mechanic is to optimise production in your vault. That means putting the appropriate dweller in a room - say putting a dweller with a high strength rating in the power plant to speed up power production, or high agility to speed up food production. As you build out your vault and increase the population, more rooms are unlocked. Things like a radio station to lure in new dwellers from the wastelands (you can also couple your dwellers to create second generation dwellers), training rooms to raise the S.P.E.C.I.A.L. skills of your population, and improved versions of the rooms where you gain resources (power, food, purified water).
Naturally there are dangers. Any room in your vault can be invaded by Radroaches or molerats, and raiders and deathclaws attack your vault from its entrance. There are also fires to extinguish. There is an element of micromanagement here where you can move dwellers around to deal with emergencies. Ultimately you'll want to level up and gear up your dwellers enough so they can make long treks in the wastelands and bring back rare items. It's really a pretty neat text-based non-interactive version of exploring the wasteland in any Fallout game that you can follow as your dwellers exit the vault. You can tell them to head back at any point, but preferably before they run out of life, stimpacks and radaway. Even if the events grow somewhat repetitive, it's still fun to read up on what happens, and the level of the character as well as his or her S.P.E.C.I.A.L. skills determine how they play out.
Having spent an unhealthy number of hours managing our vault there can only really be one conclusion. Bethesda have nailed the concept. Simply put it's highly addictive fun. There is a ton of depth and you can really tell there is a plenty of love and attention to detail that has gone into creating this game.
It's difficult to review any "free", "free-to-play", "freemium" title without it turning into a review of its monetisation model. Fallout Shelter sidesteps this in some ways, the lunch boxes work much like card packs in collectible card games and you clearly earn enough free boxes to have a great experience without ever paying for extra. And there's Mr. Handy who can be used to collect resources on one floor of your vault automatically, or be sent out to collect caps in the wasteland. Fallout Shelter is a very generous free game and while there is grinding it's not in the game just to create friction and coerce the player into spending money.
The flipside of this is that little thought has been spent on creating a meaningful end game once you have your economy set up properly and have reached the population cap of 200. Sure there are more rare items to collect, but once you've equipped your dwellers with great weapons and suits, and have levelled up their skills to a point where fending off Deathclaws is a breeze, then there is very little challenge left.
In summary, Fallout Shelter is just as advertised; an addictive Fallout themed simulation full of charm and character that can be played without paying anything beyond the non-existent entry fee.