I'm sure that ModDB got some interesting levels for HL2. About adding - You must download them to folder with steam games (because hl2 require steam) and some mods will be listed there as new games.
The spam was already deleted, but the Grez's reply remained.
Remember, the entire HL2 section is for spammers.
Strange, every time I try to quote you it always ends up like this:
Remember, HL2 is for spammers.
Hey... some of us are Half-Life 2 modders