In addition, ICANN the organization will have new accountability measures that will allow the community to challenge decisions it makes. It provides new powers like spilling its Board under certain circumstances.
One of the main drivers to change the current setup is NTIA's role above is seen as undue US government influence in what should be a purely technical operation by many. Over the years some have advocated fundamentally altering how ICANN works (like moving it to the UN) because of the US Government's influence. By transferring the primary oversight role to the multi-stakeholder community (users, business, non-profits, etc.) who have always really driven ICANN's decisions anyway, it is hoped that that criticism will go away and pressure to fundamentally alter how it works will dissipate.