Although i wouldnt really call Blitz3D's game engine 'minimal' as without it's engine functions theres very little left either. The entire 'language' is built -around- that engine. So the engine -IS- more or less B3D.
I say it's minimal, because it's so simple (doesn't include particle code, physics integration, etc.), I had to write my own engine layer in Blitz3D when I made Blitz3D games, and implement my own scripts, etc. from Blitz3D.
The HL2 engine probably isn't as minimal, because somehow I doubt you could make a flight simulator, or a space combat game with it. It's locked into the FPS style levels and gameplay, because I'm sure a lot of that game code is done in the C++ engine. In other words, it's much more high-level than "CreateCube" and "PositionEntity".
Like I said, the line between the engine and the script varies greatly, and depending on the engine, you might be doing the entire game in script (leaving only the low-level graphics to the engine), or you might only customize some high level behavior in script (like AI, leaving the rest [controls, physics, missions, etc.] to C++).