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Just bought the game yesterday and experienced a very choppy game.

Checking the Steam forums I found one mention of similar issues, where one of the devs suggested using "-force-d3d11" as a launch argument.

This fixed the issue for me, also allowed the Windows Game overlay to display over the game.
So if you experience similar choppy performance, try running it with -force-d3d11

For Galaxy:
1. Right click the game, Manage Installation > Configure
2. Check "Custom executables/arguments"
3. Click the Duplicate button by the first default option
4. Paste -force-d3d11 into the Arguments option
5. Name it something slightly different under My Label

When you right click the game in the list, you can find your option in Additional Executables. And if this solves your issue, you could use the "default" radio button under the option to have it be the default launch option.

Thanks to Henningboat on Steam's forums for this suggestion
Thanks DrakeFox

My game wouldn't boot at all but this fixed it