Shacknews has independently verified the issues, with our own Steve Gibson being met with two separate, nondescript error codes that kept him from loading the game at all.
The bugs have been well documented on the Steam forums, with one user compiling a list of potential fixes.
The game-loading RMN40 error can apparently be nixed in Windows XP by updating to Service Pack 3. Shacknews found success with the Vista workaround, which requires an install of the Microsoft .NET 3.5 Framework (download here) and a reboot. A separate MMA10 error requires users to log out of the Rockstar Social Club multiplayer utility in order to play.
While the missing texture problems (see above image) have been attributed to corrupt graphics drivers, many users have been unable to fix the issue after a driver reinstall. The game is also restricting some users from changing their graphical settings.
Shacknews has contacted Rockstar for comment on the situation.