is reporting that the readme file from "Half Life : Opposing Force" says that the game's copy protection system is incompatible with several makes of CD and DVD drive, including the Pioneer DVD-Rom drive that I use.
For the full list of incompatible drives, check here. If you have a drive on the list, make sure that you can return the game if it doesn't work!
<rant> When will publishers realise that using copy protection systems that won't work with many gamers' drives is shooting themselves in the foot? If I actually wanted OpFor (which I don't, luckily), the only way to play it would be to warez it. Doh! This isn't stopping piracy, it is encouraging it. </rant>