Not a book but Geoff Keighley has done articles on Half-Life 1 + 2, a kind of app of Portal 2 and Alyx https://store.steampowered.com/app/1361700/HalfLife_Alyx

Not a book but Geoff Keighley has done articles on Half-Life 1 + 2, a kind of app of Portal 2 and Alyx https://store.steampowered.com/app/1361700/HalfLife_Alyx__Final_Hours/ https://store.steampowered.com/app/1361700/HalfLife_Alyx__Fi... https://store.steampowered.com/app/1361700/HalfLife_Alyx__Final_Hours/ https://store.steampowered.com/app/1361700/HalfLife_Alyx__Fi...