Short but Excellent! Well worth it, and does a really good job at continuing the story.
The story had a really nice flow and the enemy AI was quite impressive.
And the HDR is a definite welcome to the HL Saga, because Source engine has certainly became quite outdated compared to the many news games currently on the market(Far Cry, Fear, etc.) so the HDR lighting defiantly gives a fresh of breath air to Half-Life.
Good Work Valve! The wait was worth it, but I think it was bit to long for a expansion pack.