As you have noticed, most of us recommend you to not write a basic library, by the way already available around. This is time consumming and error pronning.
About OpenGL weakness, take in mind that all major GPU's providers (ATI, nvidia) and ISH which uses such GPU's make their cards compliant to both Directx and OpenGL.
Also I don't recommend you to GPU programming, because you lost portability to others GPU's than those you have programed to. Except if you are in researching top performance at any cost, which is a good reason to do that. Many researchers are using the GPU as a coprocessor for heavy math programmimg (mainly in matrix operations).
I like too very much gamedev stuff, in particular NeHe, which was better when independent from gamedev, but still good.