First impression of 277-
Stable with surprisingly good fps in a quick test with a bunch of effects on. All available vid resolutions worked with proper graphics scaling and fov. Water refraction looks incredible with much less vwep smearing and fps cost than previous build. Reflections should suck fps down to 2 then die but does not. Not much fps hit. Only issue is items popping in-and-out of reflection depending on view angle.
Fog dithering is smoother, similar in density to gl_quake engines, and only a 10% FPS hit as compared to 20% for, umm, 'brand X'.

Something is strange with the config. One of the settings (not sure which) will cause odd colors when the exe is restarted I couldn't duplicate it every time.

engwin can open rubicon2 start map but dropping surfaces. engqsb plays rubicon2 startup demo but crashes on start.
The only thing missing in this fx arsenal is makaqu-style transparent entities, func_wall alpha etc.
opengl Y2K style without losing the sharp softwareiness. Overall a jaw-dropping release.