Could you try performing a Steam File Integrity Check? This will verify the installation of SOMA to see if you are missing any files from the recent update. You can find instructions about this method by visiting the
Troubleshooting Guide, under Problem I.
If that does not work, then try opting into the beta of SOMA. I just tried running the public_beta and had no issues with it loading up. To do this:
1. Right click SOMA and click on Properties.
2. Select the "Betas" tab.
3. From the drop down list, choose public_beta
4. Once you have exited the properties, Steam will download files necessary for the beta.
To confirm you have opted in, SOMA's name in your Library will display SOMA [public_beta]