A pretty entertaining simulator that fits the Fallout franchise well but got ruined for me thanks to a reall hard achievement.
This game has 2 main parts: the vault and the missions. The vault is where you spend most of your time. Here you build different rooms, each one serves a purpose: food, water, energy, medicine, barracks, dweller training, storage, crafting, overseer office and radio station; these rooms and their upgrades will cost bottle caps, the main currency of the game. The dwellers that inhabit the vault can be obtained by reproduction, quests, lunchboxes and the radio station, you can change their names, looks and equip them with weapons, suits and pets; they will also level up by working, which gives them more health and the option to be sent to high level quests. Your vault will get attacked from time to time by enemies that will go from one room to the next until they either die or kill all your population, so make sure you put strong dwellers at the entrance and first rooms of the vault. In order to cure the damage that the dwellers receive they have to heal using stimpaks (Health) and Radaway (Radiation).
To get those guns, suits and pets that I mentioned before you need to jump to the second part which are the missions, there are campaign missions, weekly missions and daily missions, among other special ones. In these missions you will have to kill enemies in a sort of turn based combat system, there is also special enemies that deal more damage. Missions are the main source of loot, here you even get the junk that you need to craft guns and suits at your vault.
There is also sort of like a middle part to the game, which is when you send a dweller to the wasteland not to do a missions but to just explore, find loot and kill creatures for experience, you see his progress by clicking outside of the vault, the more he stays outside, the better loot he will find. Eventually the explorer will find random encounters, where you play as if you were playing a mission, just a little bit shorter. That's why I said it's kinda of like a middle part.
Moving on from the actual gameplay, as every free mobile type game, Fallout Shelter has things that can be bought with real money and make things easier. You can either buy nuka cola quantums (Currency that allows you to reduce the time it takes to craft a gun or suit, go to a mission or get back from one, finish the training of a dweller, among other things), pet carriers (That will give you one random pet) and lunchboxes (Gives you pretty much anything, guns, suits, junk, resources, caps, pets and dwellers). While all 3 of these things can be obtained by grinding objectives, completing quests, among other things, the best way to fill up on any of them is buying using real money.
This is where I want to talk about my personal experience with this game as an achievement hunter, in specific trying to get the blast from the past achievement, which requires you to have 20 legendary dwellers in one vault. While legendary guns and suits can be obtained on random missions, there are only like 3 legendary dwellers that can be obtained on specific quests. The rest of the 17 legendary dwellers have to be obtained through lunchboxes, and since I decided not to spend a single dollar in this game or just use a save editor and give myself 999 lunchboxes, I had to grind them. I would get a free lunchbox every 7 days I logged into the game, then from missions (Both campaign missions and random ones) and from completing objectives (That in many cases would take days to complete, like collecting 500 suits or guns, even when I used pets that gave a 3x objective completion bonus). I would play this game every day, some times just playing a mission and other times having the game in the background while I studied or watched a Youtube video; I had this game open in my computer for a total of 794 hours before I opened my 340th lunchbox and got the last legendary dweller. And even though I didn't wanted to use a safe editor I had to in some cases because despite the fact I made back ups of my save files, some times my saves would get deleted if the PC was turned off when the game was opened and I would lose days of progress; there was also a bug where the progress on your objectives would go back to zero, this bug would happen so often that long objectives became impossible to do, so I just skipped them and added the lunchbox via save editor.
Overall, this game is pretty decent for being a mobile game and it fits the Fallout franchise pretty good, even though I was disappointed to see there wasn't any Fallout New Vegas content in this game; I also like the fact that you can have the game in the background while you do something else. So if you want a simple game to play in your free time or in the background I recommend it, but if you are not only an achievement hunter that doesn't like having unfinished games but also one that doesn't want to use real money or cheats, I don't recommend it, it will require superhuman compromise and it will be hell sometimes thanks to bugs and lost progress.