Succeeding in certain missions will get you access to lunchboxes that will have weapons, costumes, and additional currency. These weapons and costumes can be given to your dwellers to boost their stats and help fend off raiders. Of course, it wouldn't be a Fallout game without raiders brandishing makeshift weaponry. While you can assign weapons and costumes to any dweller, I usually kept them unassigned until a raid happened and then quickly equipped whoever was closest. Most of these raids are a nuisance rather than a threat--if you have weaponry, you'll likely be able to fight them off. But you can only deploy a couple of dwellers per room, so if you have raiders crowding into your power plant, you have to micromanage who goes into the breach and takes them on. It's a clunky, often frustrating mechanic.
Similarly, while sending one of your dwellers to go explore the wasteland and find new equipment is a great idea in theory, you'll have to monitor their endurance and running log pretty closely--their battles all happen off screen and if you don't pay attention, you'll return to the game and find your explorer has died (resurrecting them is somewhat costly).
While the art aesthetic is beautiful and quirky, and the dark humor is true to the spirit of the series, Fallout Shelter suffers for its repetitive gameplay and slow pacing. With Tiny Tower and its ilk, you eventually got bored of the adorable artwork, daily quests, and the grind of collecting resources. Fallout Shelter, despite some dashes of chaos, is too slow and taxes the most important resource of all: Your patience. As a freemium game, maybe this flavor of ant farm is what you've been craving, but don't expect for this to have much of a half-life.
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