It is immutable and has versioned image releases (unlike Arch, which is mutable and rolling release).This adds stability, makes the system less prone to breakage, and easy to rollback (factory reset).

Ans of course, the biggest visible difference is that this boots directly into Steam big-picture mode, where you operate the UI using a controller (although it does support KB+mouse), which makes it ideal to use connected to a TV, like a regular gaming console.