Key features of Wine 1.5.5 include:
- Support for installing Mono as a Wine add-on package.
- Dithering of pattern brushes in the DIB engine.
- Support for installing the .NET 4.0 runtime.
- DDS files supported in D3DX9.
- Various bug fixes.
The main items are support for Mono as a Wine add-on and the .NET 4.0 run-time installation support. On a related note, Wine-Mono was recently updated.
The DDS files in Direct3D/DirectX 9.0 are important, but it's unfortunate that the level of support for this Microsoft graphics API continues to lag behind -- similar to the Mesa support lagging behind a great deal in terms of support for the latest OpenGL specifications. DDS files for Direct3D are used for storing compressed/uncompressed DXTn textures.
More information on Wine 1.5.5 is available from WineHQ.org.