In Vanilla FO4, Power Armor isn't very special. You get handed a free set in one of the tutorial quests, and keeping it running is easy, the only drawback is it doesn't really protect you very well. Life in the Ruins does quite a lot to overhaul Power Armor progression already- from blowing up the free tutorial PA, to reworking balance and progression and requiring Perks to repair it. Radfall is basically the icing on that cake, giving a few extra tweaks to how it's crafted and the related perks.
The damage formula has been tweaks so that minimum damage reduction from armor is significantly higher. The main effect of this, is that while in PA, the wearer will take a lot less damage than vanilla.
Power Armor requires 'Power Armor Scrap' to repair, which is obtained by scrapping power armor (drop it on the ground in workshop mode, and scrap it like anything else)
Material Crafting is disabled (configurable)
PA Crafting now requires Blacksmith instead of Armorer
Power Armor Repair now requires Blacksmith/Science
Nuclear Physicist - allows you to recharge Cores
Solar Powered - Reduces core usage