Do the really big games also use Open GL? Or are there some proprietary technologies out there, which can scare Open GL's pants off?
OpenGL and Direct3D both allow comparable access to the GPU.
The "really really really really really really really big games" use one of these, in addition to other non-graphical libraries, plenty of skilled programmers, artists, musicians, game designers, level designers and other staff to create those games "that cost billions to develop".
OpenGL and Direct3D are the heavy-hitters in the gaming world. Neither scares the pants off the other.
Note, however, that big game houses will use commercial game engines that hide these APIs for the most part.
Most PC games (and xbox360) use Direct3D, but some do use OpenGL.
You can find out more about Direct3D and download it all from Microsoft here... http://msdn.microsoft.com/en-us/aa937791.aspx
Feature-wise you can accomplish the same output with either API (OpenGL or DirectX). Several game engines abstract the underlying API from the developer resulting in games which can use either API and are potentially cross platform.
Some examples of this are most of id software (doom,quake,etc) games and any games which use their engine. World of Warcraft also supports either Direct3D or Opengl. Also, several steam/valve games which run on Windows, Mac, and rumored Linux.
Really big games use a graphics abstraction layer (as mentionned by basszero) since they have to target different platforms that have different APIs:
Xbox 360 : D3D9+
PS3 : libgcm
Vista/Win7: D3D9, D3D10, D3D11
XP : D3D9
OSX : OpenGL
The simple answer is that no, there's no direct alternative to OpenGL that's obviously superior. Direct3D is pretty nearly the only competitor of any kind, and while it's certainly competitive, it doesn't enjoy any major advantage.
At times, Direct3D has had something of an advantage in speed -- it's controlled by Microsoft, who could quickly modify the specification to take advantage of the latest graphics cards updates. At that time, OpenGL was controlled by a multi-vendor Architecture Review Board (ARB). Decisions about new versions of OpenGL took considerable time, and a fair number of vendors seemed more concerned about backward compatibility than taking full advantage of every new trick as quickly as hardware vendors invented them (and nVidia and ATI are sufficiently competitive that they do invent them, and quickly at that).
Since then, control of OpenGL has been turned over to Khronos Group. There's been some controversy about parts of what they've done with the specification (particularly deprecating a lot of features that quite a few people still use) but one thing is open to little question: they're now cranking out new revisions to the specification relatively quickly, so it provides access to the features of even the newest hardware.