The bottom two tiers of the pyramid refer to what many games developers understand are critical to good game design: core loops and return triggers. Core loops are the most basic elements of a game and are almost always based on simple action – reward steps which make the game fun to play. Social games, such as Farmville, made popular enhancements to the core loop principle by introducing wait steps into the loops.
The second tier, the Retention Game, relies largely on a game construct called the return trigger or return loop. Return triggers are essentially about giving your players reasons to come back and play your game and there are many different ways of doing this based on lots of different principles such as player competitiveness, rewards and achievements. The effectiveness of the different return loops depend a lot on the players that are playing the game and which Bartle player type categorises them best.
Successful freemium or free-to-play game design relies heavily on getting these looping constructs right. In order to achieve this, however, there is perhaps a more important loop that developers need to master. Anyone familiar with software development will understand the iterative nature of Agile Development Methodologies such as Scrum. Adopting this in games has never been more important. Free to play game design IS an iterative process. It is not possible to do it successfully without iterating.
Even within the main game development loop, there should be an additional loop relating to A/B or Multivariate testing whereby you segment players into groups and try different variations in parallel capturing data and analysing results before making the changes permanent.
As you can see building games today relies on mastering many different types of loops. All of them need to be right for successful freemium and F2P games but perhaps the most fundamental loop to master is the iterative game development process. It is not possible to get all elements of free to play game design right up front so once your game is launched, if you want it to make money, you will have to allocate resources to running the game which involves capturing data, analysing data and prioritising a backlog of changes to the game based on how players are playing it.