Alpha 19 is a Major improvement in US/US2.
With more models, along with better collisions and fragmentation, like tidal fragmentation.
Pros:
More models.
There's an appearance tab where you can change the colors of the celestial bodies.
Tidal Fragmentation is implemented.
Fragments have different appearances based on mass, temperature and consistency.
Flaws:
The atmospheres are still 10x too tall on the planets, Obviously if Earth were 2.54 cm in radius, the atmosphere would only be as thick as a coat of paint (excluding the Ozone layer). Plus look at the atmospheres in Space Engine or Celestia along with NASA images.
The textures are still the same, they haven't upgraded especially for the gas giants and its moons or dwarf planets (besides Pluto).
There is still no oblateness yet.
There's still no tidal bulge, yet if you let something like a Black Hole get near a star, that star would bulge significantly, but that's still not implemented yet.
Also the "sphere" resolutions haven't improved, they certainly need some improvement.
And the Pool Balls haven't had their "sphere" resolution upgraded either.
I hope you guys remembered that.
Yet it would also be good if we got an actual Death Star model along with Star Destroyers and Tie Fighters + The Millennium falcon, or the USS Enterprise.
I hope you take your time, as this is still Alpha, but it might take a lifetime to implement each thing one at a time.
Alpha 19 is great, but like always, things should keep getting better.
I hope for more in the future.