A great game indeed! Storyline was quite awesome, blew my mind at few places..
I also enjoyed the "scale" of levels, really gives you the impression of how huge the facility is..
Somewhere in the middle the tests around the old part of the facility got a bit dull (basicaly just looking around where can I shoot a portal..) but later the tests were cool again..
The ending was quite nice as well, and the song was lovely..
This mod does not work. There is no way to complete it. I got to the part where the angel says "take this key" and there was NO key. I looked everywhere but there was NO key to continue. Even the youtube videos do not show the completion of this custom story because it cannot be completed. I can't believe stories that cannot be completed are even available for download here.
Even though only the half-life parts are finished at time of playing, This game goes above and beyond what valve made and is in my opinion of the same quality as any valve released game.
In my mind this doesn't qualify as a mod, it's much more. They have included a lot of small changes that all add up to better insight into some charters and a much smoother playthrough.