The game is good but you can't buy DLCs directly through Steam store. You have to buy Rage Coin to buy DLCs.
There are 4 purchase option. (You also need Bethesda Net account)
1. 500 Rage Coin
2. 1,100 Rage Coin
3. 2,500 Rage Coin
4. 4,500 Rage Coin

A DLC costs 1,500 Rage Coins meaning that you have to buy option 1+2 to get 1,600 to buy a DLC. You will have 100 Coins left for nothing. Or you wish to buy the Digital Deluxe Upgrade for 2,000 Rage Coins. You have to purchase the option 3 for 2,500 Rage Coins which you will have 500 Coins left hoping that you can spend it on something else. And of course, you need to buy more Coins because 500 is not enough!

Or you can buy the option 4 to support their st(y)o͞oˈpiditē