The most significant part of the SCS Software 1.40 Update was the complete revamp of the lighting system.
Beyond the visuals, ETS2 1.40 focused on bringing older map areas up to modern standards: AMERICAN TRUCK PACK FOR ETS2 1.40
While ETS2 received map updates, its sister game ATS received specific truck chassis updates that often get ported via mod packs: The most significant part of the SCS Software 1