Okay okay okay. Can someone explain how this is going to work if I buy the game through GMG? Like, am I actually going to have to install a new client or will I just be able to load it up through Steam?
Yeah, just register the key GMG gives you in an e-mail the day of the game's release and plug that into Steam.
GMG does have their own client called Capsule, but you just don't need that for Steam-required games.
You'll need Capsule for any Non-Steam games you buy from them, though.
When dealing w/ Steam-required games from other places [Gamersgate, GMG, D2D, Impulse, Amazon, etc] you take the game-key you are given by the digital distributor, hop onto Steam, and register it onto Steam.
Then, you can let Steam do everything from there forward.
I'll copy and paste part of the e-mail I got from them about my order w/ DE: HR.
These are the specifics.
IMPORTANT INFORMATION:
The following information is important for downloading and playing your games:
Deus Ex: Human Revolution:
If you follow these steps you should get your game upon release.
1. Open an account with Steam (click the download url below).
2. Download and install the Steam client.
3. Run the Steam client software and log in with your Steam account details.
4. In the bottom left hand corner of the client is a "+ Add a game..." button.
Click it.
5. Select "Activate a product on Steam".
6. Paste in the product activation key (when it is emailed to you upon release
of the game)
7. After a couple of minutes Steam will authenticate the code.
8. Click on "Library". You should see you game in the Library.
9. Click on your game to start downloading it.