To begin with, there's also no support for Google Play services (GMS). There are a few limitations, and a couple of them aren't exactly trivial. Support for additional versions is already in the works, but it's unclear when the list will be expanded, and to which versions. So far, the emulator only supports KitKat 4.4.4.
They've even added a neat trick: you can install apks with drag and drop. The emulator also supports attachment via ADB, meaning you can still use familiar commands, tools, and even other IDEs. Performance isn't the only trick up Microsoft's sleeve, the emulator also supports a number of sensor simulators for the accelerometer, GPS (including route traversal), and even a live battery slider. Check out the video below to see a demonstration of the emulator fully booting in a matter of seconds.
It uses a custom x86 build of AOSP, but it has also been optimized for Microsoft's Hyper-V virtualization platform to achieve the best efficiency. Alongside the IDE is a brand new emulator, designed to run much faster than Google's stock emulator and other 3rd-party alternatives. The toolchain supports the Clang compiler and LLVM optimizations. Support for Android will be a part of Visual Studio 2015, available now as a Preview release ( download link). The announcement came earlier today at Microsoft's Connect() developer conference in New York City.