Unity 4.5 includes more than 450 bug fixes and a new module manager to help bring platform-specific hotfixes across mobile platforms.
The update also features improvements to 2D physics, a major update to the shader compiler, improved MonoBehaviour serialisation and added iOS support for Open GL ES 3.0.
Other additions and enhancements include faster scene loading, sparse textures and stereoscopic rendering for DirectX 11.
Unity has also teased new additions for version 4.6, which will include the new GUI.
You can see more details about the new update on the official website.