Factorio works because the gameplay is completely original. It scratches a building + automating + researching loop that no other game has. Many people compare it to programming or electrical engineering design - the satisfaction of automating something that used to take manual effort is great, and very addictive.

The graphics are bland and the early parts of the game feel like a pre-release / beta build, but the addictive gameplay and infinite end-game potential got it a lot of great coverage.