Welcome to the forums! I've been a programmer of OpenGL for awhile now, so hopefully I can answer some of your questions.
First off, there are a lot of AAA quality games that use OpenGL. WoW, Dead Space, Doom 3 just to name a few. It's a very capable graphics API, and plenty of proffesional game developers use it.
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As to your second question, Java works, but for writing games, I highly recommend C++, it's much faster, and will run on linux a lot better 
Oh and easier to write.
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You should check out nehe.gamedev.net if you're just learning about OpenGL.
