Offshore offers a multi-level side story of Gordon Freeman while en-route to City 17 via Highway 17 in the Scout Car.
This was a fantastic mod. I was able to play this easily in Garry's Mod, which is a big relief. More mods of this sort need to be made where there are as few custom content as possible. What the creator has made here is mostly if not completely with regular HL2 assets, and he's constructed a fun, lengthy romp through differing locales.
Really hoping that one day the creator releases another mod like this one, although I think he might have moved on. If that's so, oh well. He's left behind something I can call fun and even a little remarkable.