Fallout Shelter first came out on iOS and Android ahead of the Fallout 4 release. Naturally, I checked it out, and I later played it on Steam. I noticed that radiation reduced the maximum health of dwellers, instead of being a separate stat. I didn't know that Fallout 4 would work that way, too. I've heard that Fallout Shelter is better than Fallout 76. Granted, this is a time waster kind of game with microtransactions, but it actually works!
Fallout Shelter puts you in the role of a vault overseer; a first for the series. Your charge is building, staffing, defending, and supplying a vault of your own. Building new rooms need bottle caps and usually a certain number of people. You earn bottle caps doing almost everything. Certain vault rooms produce power, water, and food. You can have your vault dwellers venture out of the vault to gather resources. They can find weapons, armor, crafting materials, crafting diagrams, and caps. Be sure to recall them back to the vault before they die, or give them enough armor and stim packs before going out. You can also assign a team to go on quests.
Occasionally, someone will show up at your vault wanting to get in. You can accept them and put them to work. When you start, you have a few people waiting. Other times, raiders, deathclaws, or ghouls will show up and beat down the door. Sometimes, critters will burrow into the vault. They can cause quite a bit of damage, and all intruders must be put down by force. Be sure to have all your dwellers armed at all times.
The endgame is boring. When your dwellers return from a trip, they have to deposit all of their loot into the vault inventory. If your inventory is full, they must stay outside until you free enough space. There is an option to automatically sell common items, but that only goes so far. I suspect that it might not sell every common item they carry. Further, if they have a crafting diagram that you already have, it takes several seconds to dismiss each one. If they bring in 5, it is tedious.
To get the most out of your dwellers, you need to manage their happiness. This is supposedly related to their highest SPECIAL stat, but I'm not sure. Each individual will be happiest when working a room that uses that stat. Long after wondering how to manage it, I thought to give dwellers a middle initial of whatever stat was their highest. If you have a high daily average of happiness, you get a bonus, usually caps, lunch boxes, or Nuka Cola Quantum.
I have a vault that's full of demigods with maxed out SPECIAL stats, and they all have enough power armor and plasma rifles to make the Brotherhood blush. There is a survival mode where dwellers can't be resurrected, so that's what I did with my next vault. I had forgotten how depressing it is to get off the ground with people dying left and right, so I stopped playing and started writing this.
The graphics aren't flattering, but the anisotropic filtering and antialiasing settings in my graphics driver have no effect. The animations are probably better than any Todd Howard game.
It's a good game to play on the side while you're watching Youtube, like 20,000 Lightyears Into Space. If you dedicate your full attention to it, you will get bored fast. It's decent for being free and I can't argue against it.