lessons learned from Halo 2

1. You can turn 30 seconds of fun out into an entire game by repeating it over and over again.
2. 160 pages of (120 minutes) cinematic for 20 hours of game play is too much cinematic.
3. Game levels must be able to accommodate different abilities, such as how the player in Halo 2 navigates the sentinel headquarters by walking, where as the sentinel can fly.
4. Electronic Entertainment Expo (E3) is the biggest trade show in the game industry so it is important to have a demo to show there to get people excited about your game.
5. High quality graphics makes the frame rate go down, which decreases the quality of the animation and the timing with the music. Overemphasis on the graphics can lead to a polished game with lesser quality game play.
6. New features such as giving characters the ability to interact with vehicles can improve a game.
7. Every element added to the game, as well as highly detailed graphics, can slow down the frame rate.
8. It is important to generate enthusiasm for the game early in the game's development in order to sell as many games as possible during the holiday season when it is released.
9. If your game has vehicles, the players should be able to get into them and use them.
10. Deciding to focus on detailed real-time graphics can cause a project to miss deadlines.
11. Using live reference is the best type of research.
12. People like to play games together and socialize, and good games foster this.
13. It is important to keep the scope of the game small enough to be able to complete, it may be necessary to cut out parts of the game. 
14. Level diagrams can'te be changed once set.
15. The time line should schedule a lot of time near the end for play testing and bug fixing.
16. Give your voice actors detailed background stories.
17. Having a fixed deadline forces team members to finish and gives a goal to work towards.
18. All the different elements of the game depend on each other, but are created by the different departments and it can be chaotic to combine them into a functioning game.
19. Plot holes make a game far less enjoyable.