Actually, there are more reasons to avoid the HD version of The First Encounter than to "upgrade" to it. Most notably, the game is incredibly buggy at launch. Incompatibilities with video and audio drivers have caused trouble for many users. Some even make the game virtually impossible to play. A quick glance at either the Croteam or Steam forums reveals how many gamers are having trouble. We ran into the main sound glitch noted online where the game crashes constantly due to a bug with audio sample rates. Both Windows XP and 7 were affected here, with the game locking up so frequently and even forcing occasional system reboots that it was unplayable. Even the first patch did nothing to rectify this problem. You can play the game fine with sound disabled in Windows, but that isn't a reasonable fix. Only editing an obscure line in the game's configuration file seems to clear up the issues. All in all, we spent at least six hours struggling with this annoying issue--which, coincidentally, is about the same amount of time it takes to finish the single-player part of the game. Croteam obviously kicked this one out the door long before it was ready for primetime.
