This is the only magazine to my knowledge that deals with business practices as well as technical topics of game creation. GDM has postmortem on recent successful games, summarizing how these games were made, what the creators did right and what they could have done better. They also has columns devoted to Project Management, Game design, Graphics technique, Product reviews and trend analysis.
All in all this is a must have if you're in the game industry or, like myself, dream of being in the game creation business. Most of the time these articles do not go into a lot of details because of length constrain. That might be the only drawback.
Good Magzine but get it for free
This is one of those industry trade journals that they "charge" for but if you are in the business send for free. Visit their site and see if you qualify before you pay for a subscription.