Good idea, great art!
Lack of sound is disappointing. The combination of the boulder that spawns close to the portal, the lack of boulders in general and the difficulty of mining anything once 2 or 3 enemies catch up to you means that the only way to do anything is to just farm the first boulder and run back to the portal, which isnt very fun. It would also be nice if the portal had an indicator instead of the coordinates.