Up front, the new Sonata looks much wider than the current model. Part of this is due to the headlights being moved to sit inline with the top of the grille, as opposed to slightly above on the current model. And while we can't see it clearly, the grille will likely have a similar shape to that of the current model and other Hyundais. The fenders also wrap around the top of the car more, further contributing to the car's wide stance.
The profile of this new Sonata is different, too. It's a bit more traditional in how the engine compartment area doesn't blend into windshield as much. The current Sonata blends the engine, passenger and trunk compartments more. There's also a curve to the bottom of the greenhouse on the new car that lends the car a more graceful, less upright appearance. There is still a fastback look to the rear of the Sonata, but it's stretched out more, again helping the car look less upright.
This is the first time we've seen the next-generation Hyundai Sonata, but it does look as though it's pretty far in development. What we can see of it appears to be production ready. As such, we probably won't have long to wait to see the car revealed. It will probably show up sometime next year in time for the 2020 model year.