So I'm quite baffled with Steam problems with Wine at the moment. I've read through other threads and help places in here and on other forums (Steam, Reddit...), and I'm still getting nowhere. I'd appreciate the help as I'm a newbie at Wine and don't quite get what's going on.

So I have an iMac Early 2008, OS 10.8.5. Wine seems to run just fine on it and programs generally. Steam also appears to run fine. The problem arises when I try to play any game through Steam.
Steam will download games just fine, as far as I can tell. Once the game is downloaded, though, depending on the game, I get one of a variety of errors...
One game will tell me, "The Steam servers are too busy to handle your request for Sid Meier's Civilization V. Error Code (55)"
(this is nonsense, as it works fine on the Mac itself or when I run Boot Camp)
Another game will tell me, "Unable to find critical file - unable to load up gamedata.dat. Closing."
When this happens, I go to Steam and check the integrity of the game cache. Steam indeed finds that there is a file missing - Steam downloads the file, and then I try again. Once I boot, again - it is unable to find the file, which has mysteriously disappeared.
I suspect all the other games will be having similar problems...
What's going on? :/