So I'm probably not the best person to answer this, I've only been half following it. I don't watch every video and livestream, so my details may not be all correct or up to date.
The Dungeon Coach (The DC, in DC20) is a D&D YouTuber. I don't know where he ranks among them but he's not the biggest out there. I think he's got like 50k subs, so not even close to the big timers like Colville, Ginny Di, or Dungeon Dudes. Up until DC20 he mostly made content about home-brewing 5e. I purchased his first KS book and it's like a home brew supplement Dungeon Master's Guide. It is just chocked full of different random problems and alternate ways to run them. Initiative, Chases, Heists, etc.
What interests me about DC20 is that it feels like he is rebuilding 5e, while not being afraid to kill come of the sacred cows. It has trimmed down the abilities to four scores, two physical, two mental. On top of that it he's cut the ability score/modifier system, in favor of just a single number. I think it's -2 to 4 maybe?
He's introduced Action Points. So rather than having a move action, a combat action, a bonus action, etc. You get a number of points. You could use all of your action points to just move, move, move. Or attack, attack, attack. Or move, attack, move. I believe you can also essentially 'upcast' actions to give yourself advantage. Like your attack is one action point, but you could use two to make an attack with advantage. I believe Pathfinder 2 uses a system like this? I think it sounds good.
Got rid of spell slots in favor of a spell point/mana pool system.
He's tried to make the racial and class options more flexible and customizable. Rather than picking a race there's an ancestry system. You pick your race, and it'll have all of your standard options. Elves are dexterous, have dark vision, what ever. You then get the option to customize this with a point buy system. So if you don't want to be a dexterous elf, you could drop that trait and use the point to buy a different one, perhaps strength or intelligence. There is also the option to take a negative trait, and get an extra point to purchase more or better positive traits.
Multiclassing will have a similar customization system. Rather than alternating between fighter levels, and wizard levels to make your gish spell sword, you could make a fighter, and opt to take a selection of wizard abilities instead of fighter abilities as you increase in level.
There's plenty I'm missing, but this are some of the features that spoke to me. I'm interested in seeing the final product.
Like others have said getting information on it hasn't been the easiest, but it's currently in the alpha phase.. Once the kickstarter launches I'd hope he has a better, and more fleshed out pitch for it.
