Freespace 2 with Source Code Project & FS Upgrade Project
Theive redone models, graphics & some mechanics with DX8 or OpenGL
You can play through the original campaigns (fs1 & 2)
There are about 3-4 very very professional fan made campaigns that are worth the time
also there's a Babylon 5 rework and a Wing Commander one .. and i think a star trek one too
i recommend FS1 & 2 to anyone who liked Wing Commander series (on a medium difficulty at least - do note that the default is easy) - the story and feel is terrific -