You should not be seeing that loading screen. It was replaced before the game was released.
A couple other people have recently reported this same problem. In two cases it was fixed by installing the game to a different location. One person (who was getting a crash at that point) mentioned installing it on a different drive, while the other (experiencing an endless loading screen) just said they uninstalled, got rid of anything D:OS related they could find, and then re-installed to a different folder. A third person (endless loading screen) didn't report back if these suggestions helped, or not.
Maybe try moving the install folder to a different location (outside the Steam install path), and starting it directly from the '..\Divinity - Original Sin\Shipping\EoCApp.exe' program file.
Steam has a backup function, so you may be able to backup/restore the game to a different location, rather than reinstall and re-download. If you do try reinstalling, you may be able to skip the download part by pausing the download when it starts, copying the install folder (previously copied or moved) to the new location and then verifying local files in Steam.
Also, you could try checking your hard drive for errors, to make sure there is not a corrupt file or something from the alpha carrying over into the release version (in Windows Explorer, right click on the hard drive, select Properties and under the Tools tab, Error-checking section, click on the 'Check now' button).
