This is literally Visual Studio "isolated shell" modified by Atmel to work with both 8 bit and 32 bit AVR chips. The compiler is the AVR GNU compiler and its toolchain. Since WinAVR is a dead project, Atmel is providing updates to the GNU toolchain so it supports the latest Atmel chips.
Visual Studio is much better than even Eclipse, Netbeans, Codeblocks, Programmer's Notepad, Qt, KDevelope, and a whole bunch of other IDEs I've used in my life.
So what are you waiting for? Move on to greener pastures already.
I'm using it and it's blowing me away. Some things I find missing includes avrdude, but I can add the commands as "external tools", also there's nothing to assist me with fuse bit settings. I'm not about to drop my AVR Project IDE yet but I'm thinking about it.
Installation is an epic long process though, a big download too, just a heads-up.