All the original tracks.
Most of the original music (there are apparently a couple tracks they couldn't get)
Developed by Vicarious Visions (Crash and Spyro remasters)
Essentially a remake branded as a remaster in typical VV style.
Almost everything is being remade from the ground up, VV was only able to get handling information from the old games.
The goal is to get as close to 1-to-1 as possible.
Online multiplayer, new challenges, character specific challenges.
September 4th for $40
Pre-ordering gets early access to try out the Warehouse demo sometime this summer
Looks to be Epic exclusive on the PC, otherwise coming to PS4 and XB1.
This IGN video has a little more info, including a couple things I mentioned above