[Mysticpuma]

"Purchased today (getgamesgo.com), downloaded game, installed and verified steam account, but when I put my game key (which I received on email) steam says it not a valid code...???"

Okay, I think I misread what you did, as I got mine through Steam, not from a retailer.

So, what you may need to do instead is;

Open Steam (double-click icon), click on Games Library, Add a Non-Steam Game to my Library, browse to that game, then tick the box next to it, this will add it to your library, click on Games Library, Click on CD Key (on right of window), Click on Copy to Clipboard (as this number is different to your activation code), Paste into "Please enter your activation code here" window, "Enter", Activation Successful"."

Alternatively;

Open Steam (double-click icon), click on Games Library, Activate a product on Steam, Click Next, Enter your download Key that you got to download from Gogamer, Click Next (you should get a product activated already, or thankyou for adding, or downloading updates from Steam....or something similar?). Once that is done click on Games Library, Click on the Game IL2: Cliffs of Dover, Click on CD Key (on right of window) it should say or online activation number is (or something similar) Click on Copy to Clipboard (as this number is different to your activation code), Paste into "Please enter your activation code here" window, "Enter", Activation Successful"."
, Click on CD Key (on right of window), Click on Copy to Clipboard (as this number is different to your activation code), Paste into "Please enter your activation code here" window, "Enter", Activation Successful"."

I am guessing this, as I didn't purchase/download it from outside of Steam, but once you click on CD-Key, it should give you an online activation number, which you then Click on Copy to Clipboard (as this number is different to your activation/download code).

I hope that helps, but other than that, it may be down to others who have downloaded outside of Steam to get involved?

Cheers, MP