Union market, navy yard, buzzard point and the wharf will all be nearly unrecognizable to you likely. (Though I doubt you went there before. You will go there now.) the Anthem will be the best place to catch bigish acts. It's a great venue that DC sorely needed.

More bike lanes. Bus lanes. Soon to be bike lanes in Connecticut Ave.

The dome on the Jefferson is white again lol.

Generally speaking, a lot of empty lots are now buildings. And some of your favorite businesses might be something new.

NW got a Wegmans which is cool I guess.

There's an Eisenhower memorial that you'll barely notice, and a WWI memorial that's almost just as forgettable.

Oh and anywhere near the white house, congress, or supreme court will have more fencing/security than you remember.

Edit: oh and silver line to dulles. Plus purple line is coming (2030 probably....)