I think trading card games like Gods Unchained and Sorare have a great future ahead. Both work on ETH, but you only pay transaction costs, when you're loading up your ingame-wallet.
Gods Unchained created a layer 2 solution completely on ETH and the market startet booming.
There's also a lot of realestate games like dCity and Upland. One of those will surely explode. It's just too much competition and no clear market leader.
Sandbox could have a great future, when it start letting people actually play.