The press release lists the following enhancements available in OpenGL 4.0:

•two new shader stages that enable the GPU to offload geometry tessellation from the CPU
•per-sample fragment shaders and programmable fragment shader input positions for increased rendering quality and anti-aliasing flexibility
•drawing of data generated by OpenGL, or external APIs such as OpenCL, without CPU intervention
•shader subroutines for significantly increased programming flexibility
•separation of texture state and texture data through the addition of a new object type called sampler objects
•64-bit double precision floating point shader operations and inputs/outputs for increased rendering accuracy and quality
•performance improvements, including instanced geometry shaders, instanced arrays, and a new timer query