Here we'll cover the phases from Pre-Production to Production and yet to Service.
This image shows you the structure of preproduction and the phases in it. Also, it shows the nature of iterations happening all the time.
Inside the black boxes I listed what you should nail at which point.
Today creating a game is pretty Agile and Scrum is used in some way in game companies.
In practise what happens, it can be a combination. We have milestones set and towards those we go with sprints from scrum. Each sprint can last 1, 2 or even 4 weeks.
The games out and that's it? This is where it all might start. The game is doing well, but it needs to be fixed and updated. You might be releasing an update even every week. It can mean hectic and busy time at the office!
If you just let the game, so will the players. If they feel the product is dead, you'll lose them.
At this point game is developed based on metrics, feedback from players and results from A/B testing. In A/B testing every second player gets some part of the game presented in a different way than the other players. Results are checked to see which of the two methods works better.