iMac 3.2 GHz Intel Core i5, 8GB DDR3, Nvidia GeForce GT 755M (1GB Dedicated), running OS X 10.9.4
Tried multiple varieties of settings, as well as lower resolution and graphics and disabling features. Game is running through Steam for Mac (not beta).
Still get nothing but the black screen (after the Frictional Games Logo displays) and music.  Please patch this for these newer machines 

    HPL.LOG below:
Version 1.20
-------- THE HPL ENGINE LOG ------------
Engine build ID 20110513121655
Creating Engine Modules
--------------------------------------------------------
 Creating graphics module
 Creating system module
 Creating resource module
 Creating input module
 Creating sound module
 Creating physics module
 Creating ai module
 Creating gui module
 Creating generate module
 Creating haptic module
 Creating scene module
--------------------------------------------------------
Initializing Resources Module
--------------------------------------------------------
 Creating loader handlers 
 Creating resource managers
 Adding loaders to handlers 
--------------------------------------------------------
Initializing Graphics Module
--------------------------------------------------------
Init lowlevel graphics: 1024x768 bpp:32 fs:0 ms:0 gpufmt:2 cap:'Amnesia - The Dark Descent - Loading...' pos

-1x-1)
 Setting video mode: 1024 x 768 - 32 bpp
 Init Glew...OK
 Setting up OpenGL
  Vendor: NVIDIA Corporation
  Renderer: NVIDIA GeForce GT 755M OpenGL Engine
  Version: 2.1 NVIDIA-8.26.26 310.40.45f01
  Max texture image units: 16
  Max texture coord units: 8
  Max user clip planes: 6
  Two sided stencil: 1
  Vertex Buffer Object: 1
  Anisotropic filtering: 1
  Max Anisotropic degree: 16
  Multisampling: 1
  Texture compression: 1
  Texture compression S3TC: 1
  Auto generate MipMaps: 1
  Render to texture: 1
  Max draw buffers: 8
  Max color render targets: 8
  Packed depth-stencil: 1
  Texture float: 1
  GLSL Version: 1.20
  ShaderModel 2: 1
  ShaderModel 3: 0
  ShaderModel 4: 0
  OGL ATIFragmentShader: 0
Setting up G-Bugger: type: 0 texturenum: 3
 Adding engine materials
 Initializing DevIL
  Vendor String: Abysmal Software
  Version String: Developer's Image Library (DevIL) 1.6.8pre Aug 22 2010
  Version Number: 168
 Adding engine post effects
--------------------------------------------------------
Initializing Sound Module
--------------------------------------------------------
 Initializing OpenAL
  Available OpenAL devices:
   0. Built-in Output(OpenAL default)
  Trying to open device 'Built-in Output'... Success!
  Number of mono sources: 32
  Streaming setup: 4 Buffers x 262144 bytes each
--------------------------------------------------------
Initializing Game Module
--------------------------------------------------------
 Adding engine updates
 Initializing script functions
--------------------------------------------------------
User Initialization
--------------------------------------------------------
--------------------------------------------------------
Game Running
--------------------------------------------------------
Fixed!  Found the answer on a Steam community forum and was ridiculously easy. Really seems like this should be added to the locked Troubleshooting Guide post at the top of this forum.
I spent an hour reading and trying things before finding the solution elsewhere.
If you're experiencing this problem and you're running the game through Steam, right click on the game from your games list and go to Properties, then uncheck the box under the General tab for "Enable Steam Overlay in Game".
Problem solved!  I know this will work for the majority of people with issues...hope it does for you!