You've got some misunderstandings of what OpenGL is and what it does. Read this:
http://www.tomshardware.co.uk/does-l...w-14534-2.html - the key point is: "
superior graphics have more to do with the creative skills of the game developers than the choice of API".
OpenGL does not render a game in low quality, and nor does it render one in high quality. Your graphics card renders the game. All that OpenGL or D3D do is provide a means of telling your graphics card what to draw and where to draw it, your graphics card does the rest. So, if the source artwork and other game assets are low quality the end result will be low quality.
Unfortunately not many games use OpenGL in the PC space these days so myths get out. But OpenGL is capable of doing everything that D3D can do.