There's been so many little updates it would be impossible to list, but it's rock solid, has a bunch of interesting maps, several game modes, and a seriously brutal AI system. The tech trees are entirely different to RA2, there's new buildings inserted, and the YR capurable neutral techs have been repurposed to unlock even more units (rather than their unavailable functions) to give you a wealth of options.
For bare knuckles deathmatch with another human, the War of Attrition game mode disallows engineers and spies... there's also Ground War (aka Meatgrinder) that disallows navy and airforce, but hovering units like Kirovs and Rocketeers are still allowed.
Maps have all received attention regarding ambience, all new sounds and animals to add that extra immersiveness, in the brief moments you get to scout around between apocalyptic battles.
Although the mod requires RA2 and not YR, renaming most YR winter and temperate maps to .mpr will work flawlessly, as all the YR sounds and updates to the arctic terrain (such as ice cliffs) have been included. Only in the case of some advanced map scripting or use of non-existant buildings could cause it to choke, most likely. The urban terrain has been extensively revised and updated, one of the core features of the mod, so existing RA2 and YR urban maps will be hit or miss depending how they were drawn, many of the rubble tiles were repurposed for better things for example, and buildings with zero strength should be used instead.