Apart from having one of the finest engines in the business, including Havok physics, HL2 has plenty of other stuff to show.
The way the story is delivered. It doesn't steal a style from graphic novels, books or movies, it has its own. The more you look around, the more you find - like the ape/man/combine graffiti.
The control model is damn near perfect. It doesn't feel too fast or too slow. It's easy to get on and off ladders. Little bits of polish like that.
The vehicles are easy and fun to control (particularly the crane :D ).
It makes good use of the Havok physics. Puzzles like the crane, and the plank and concrete blocks, for example.
It's easy to create mods for.
Sentynel - Head Ninja, Admin, Keeper of the Ban Afrit, Official Forum Graphics Guy, and forum code debugger.
A still more glorious dawn awaits, not a sunrise, but a galaxy rise, a morning filled with 400 billion suns - the rising of the Milky Way