This game is a lot more cartoony and blue/orange than Half-Life 2, which had a very distinctive low-saturation photorealistic style. However, it's less cartoony than half-life 1. It's fitting that a game set between them chronologically would mix their art styles.
The graphics on the promo website are a lot higher resolution than Half-Life 2's graphics. HL2 was photorealistic not by having a high polygon count, but by having desaturated textures that approached the things you would find in a picture of a city. HL2 came out a long time ago.
