Fallout Shelter was the surprise hit of the summer in mobile games, briefly surpassing Candy Crush Saga as one of the top-grossing titles on the app stores. But it quickly fell off the lists because players ran out of content.

Now Bethesda Game Studios is playing catch-up for the game, a rare hardcore hit on mobile in which you build a large fallout shelter in the wake of a nuclear war. Today, Bethesda released an update for Fallout Shelter on Android and iOS devices that should bring players back and keep them busy. In doing so, the company is trying to deal with pent-up demand and turn the game into an ongoing service, rather than a one-time experience — and help excite players for Fallout 4, which debuts November 10 for PlayStation 4, Xbox One, and PC.

It has a new Vault-Tec mode, extra tools and new features.

Like the Tiny Tower game it is modeled after, Fallout Shelter is a building and resource management game, where you have to carefully add rooms to your shelter and put people to work inside it. You can level up the rooms and its dwellers. You can send adventurers out into the wastelands to collect special items, weapons, and resources. Every now and then, you may face attacks.

The game has a look and feel that matches the well-known Fallout brand that millions already love. They’ve been waiting for years for a new Fallout, and the pent-up demand is huge. This has the same comical 1950s humor of the Fallout games. Fans have shown they are loving their first taste of a mobile Fallout experience. And they’ve shown they’re willing to pay for things.

I played it a lot when it came out, but like other players, I ran out of things to do. I hit the maximum number of 200 dwellers in my shelter, and that was pretty much it.

Fallout Shelter E3 2015 - Dweller

Above: Fallout Shelter

Image Credit: Bethesda

The notable thing about the game is that the monetization isn’t pay to win. You don’t get hit with paywalls after a certain amount of time. You don’t have to pay for energy to keep going. You don’t have to spend a penny.

You can now save your Vault to the “cloud” and then continue the Vault game on any of your mobile devices. There are also sightings of a “mysterious individual” around the Wasteland, and Vault-Tec is offering a bottle cap reward for positive identification. That means there’s somebody interesting to find outside of your shelter.

After its release in June, Fallout Shelter was the top downloaded game in 48 countries and the top downloaded app of any kind in 25 countries following its release. Bethesda drew a lot of attention to it by releasing the mobile game during its E3 2015 press conference, when millions were watching a livestream.

Fallout Shelter E3 2015 - Raiders

Above: Fallout Shelter ruled the app stores — for a short time.

Image Credit: Bethesda