The default Half-Life 2 maps are massive and linear. The community has converted them into "sandbox-friendly" versions. Search for:
GMod’s lets you pit Half-Life 2 factions against each other: half life 2 gmod content
The reskins the standard fast headcrab into a pale, teleporting ghost girl. Because the Source Engine handles lighting and shadows so well, even old assets become bone-chilling when stripped of context. The default Half-Life 2 maps are massive and linear