Even though I live in DC, this really does not effect me much.
Accessory apartments: It will be legal to rent out a basement or other part of a house in many areas where it wasn't legal before. Homeowners who want to rent out a garage or carriage house will still have to go through a hearing, but will have an easier time getting approval. This will let DC add more housing in ways that have little impact on neighborhoods.
Parking minimums: New buildings, especially near Metro and frequent bus lines, will be able to build less parking in keeping with newer data on how many people actually drive. This will drive down the cost of construction and potentially make some lower-cost new housing possible where it wouldn't have succeeded before.
Corner stores: It will be possible (though not trivial) to open grocery stores in residential row house areas, subject to a lot of restrictions. There will also be a more difficult path to open other kinds of stores. This might give residents a new way to get food without having to drive a long distance.
Expanded downtown: The downtown DC area is much larger than just the part around Metro Center, and the zoning now reflects that, incorporating NoMa, the Capitol Riverfront, and other high density central areas in the Comprehensive Plan.
Source: GGW
DC's zoning update finally passes! - Greater Greater Washington
I am glad this finally passed. Long term it is hard to read the impact, but I do not see this as a huge change. The height limit was not increased, as a result I think even with these changes they are overall minor in overall impact. There may be a few more english basements around town, but otherwise not a huge shift.