He'd previously made new versions of the levels as an add-on for the free mod version of Black Mesa, and has good things to say about how and why they've expanded Surface Tension in the commercial release.

LambdaGeneration had a good interview in January with Black Mesa mapper Chon Kemp about Surface Tension Uncut. It’s a very important part of the Half-Life story.' The end of ST is the part where the H.E.C.U start to lose, and it sets up the events for Half-Life 2. 'Surface Tension did not feel complete without its later levels. Three levels were missing before, and all in all Surface Tension is now about an hour longer. It has the dam, the cliffs with the fly-by, big battles between the aliens and soldiers, that airstrike puzzle, and lots of other big set pieces. Surface Tension, to refresh your memory, is the chapter where Gordon has escaped from the bowels of Black Mesa and jaunts around on the surface. it sounds like a cracker of an update for a game which was already great. They've also added dynamic shadows to outdoor areas, revisited and polished-up some levels, massively sped up loading times, and. Over the weekend they released an update heavily expanding the 'Surface Tension' chapter, adding back areas that didn't make the cut before. The alien world of Xen is the biggest part of Half-Life still to come to its fancy remake Black Mesa, but developers Crowbar Collective have been working on plenty more.

Half life surface tension