-ID3D11Device1, ID2D1Factory1, IDWriteFactory1, IDXGIFactory2, IWICImagingFactory2, ID3DUserDefinedAnnotation and related APIs are available
-Improved Direct3D 11 device interoperability via ID3DDeviceContextState, including the improved interop with Direct2D/DirectWrite
-D3D11_FEATURE_DATA_D3D9_OPTIONS feature detection
-In addition to the new Windows 8 WIC features, this update also fixes decoding of 96bpp floating-point TIFF images.

    -Feature Level 11.1 hardware
    -All D3D11_FEATURE_DATA_D3D11_OPTIONS features for Feature Level 10.x/11.0 devices
    -16bpp format support (DXGI_FORMAT_B5G6R5_UNORM, DXGI_FORMAT_B5G5R5A1_UNORM, DXGI_FORMAT_B4G4R4A4_UNORM)
    -Tile-based Deferred Renderer optimizations (D3D11_FEATURE_DATA_ARCHITECTURE_INFO)
    -HLSL minimum precision shader optimizations (D3D11_FEATURE_SHADER_MIN_PRECISION_SUPPORT)
    -DXGI 1.2 features for Stereo, Occlusion status notifications, Desktop Duplication, and NT Handle shared resources
    -Windows Store app ICoreWindow features of DXGI 1.2
    -WARP support for Feature Levels 11.0 and 11.1
    -Direct3D hardware support in Session 0
    -The DirectComposition API

The situation seems a bit awkward, as it appears that some features (like the minimum precision shader optimizations) would be great if ported to Windows 7. The reason for not porting them - according to various reports - is due to the absence of WDDM1.2 on Windows 7, and from what I know so far, MS is not planning to release WDDM1.2 on its older OS.