Here are the killer features that make v20 "better":
: One of the primary goals of the 2.0 ruleset is to make the game more straightforward and quicker to play. This has been achieved by clarifying rules interactions, reducing the number of exceptions, and making the objectives of the game clearer.
The transition to Horus Heresy 2.0 (often called the Second Edition or Age of Darkness) significantly altered the game's flow, making it feel more interactive than the previous 7th Edition-based system. While some players prefer the "crunch" of 1.0, the general consensus is that 2.0 introduces streamlined mechanics that reduce downtime. Key Improvements in 2.0 The Reaction System
: The dedicated psychic phase was removed. Powers are now resolved via Leadership checks when activated, preventing players from "checking out" if they aren't playing a psychic-heavy army. Increased Lethality