1. Put Gameplay First
2. Make Your Games Easy To Learn, Difficult To Master (cited Guitar Hero as a good example of this principle)
3. Resist Pressure To Ship Early ("Nobody looks back on Diablo and thinks 'How much better it would have been if they had released it three weeks earlier'", Morhaime said.)
4. Resist Pressure To Do Everything At Once
5. Estimate Demand (Finding out how many people have the technology and Internet infrastructure available to play your game.)
6. Human Resources Is Important (The success of WoW led to a massive scaling up of the Blizzard.)
7. Running An MMORPG Is Not Just Games Development (24/7 IT, customer service, and community management are essential elements of a successful online game.)
8. Communicate Or People Will Make Stuff Up (Make sure your company has teams dedicated to keeping the community and internal company figures informed of bugs, fixes, and other games issues).
9. Avoid Financial Incentives (Minimize financial rewards from gaming sweatshops, credit card fraud, and account stealing.)
10. Test (Blizzard's testing process involves three steps - everyone at Blizzard plays the game, a public beta is launched, a test site with dedicated test server is set up.)

Via Wired