Analysis of Game Concepts and Player Learning in Portal

An examination of how game concepts in Portal are introduced to the player over the course of the game. The purpose is to better understand the balance and difficulty of the game for application and comparison with other games.


The following will examine how game concepts in Portal are introduced to the player over the course of the game. The purpose of this examination is to better understand the balance and difficulty of the game for application and comparison with other games. The ultimate goal is to reach meaningful conclusion as to what is considered “good application” of game concepts over the course of a game.


There is no objective accuracy in the details of this analysis, as it is purely subjective and based on my own perceptions and enjoyment factors. Further to this, the quantified “number of concepts” is not exact, and it could be argued that they should be presented at a level of granularity higher or lower. But they are not.



Portal is a good video game, and worth analyzing. If you don’t agree, you probably won’t agree with the rest of this, so stop reading now.



For the sake of this analysis, the terms “Level” and “Test Chamber” are the synonymous. Levels “0a”, “19b” through 23/”Boss Fight” are not actually in a Test Chamber at all.


For each level in the game, a set of notes were taken on concepts learned through mandatory teaching in the test chamber. For example, as soon as the player gets the portal gun, they can shoot a portal anywhere on the wall. But they are not forced to do that to solve the puzzle. The elaborated concept “I can shoot Portals onto any part of the wall” is not required to solve a puzzle until Test Chamber 3.


It’s also worth noting that any narrative concepts (e.g. The presentation of GLaDOS glitch and nefarious nature) do not count as “game concepts” in this context.


Game Concepts: Brand New vs. Elaboration/Combination

Something in the game is considered a brand new concept if the player has never seen it before. For example, in level 0, portals are seen for the very first time. However, in “Test Chamber 01”, portals are no longer static, but move automatically around the chamber. An existing concept (Portals) is elaborated on (Portals can move places).



  • "I can walk through Portals" (Brand New)
  • "I can pick up Cubes" (Brand New)
  • "I can carry Cubes through Portals" (Elaboration/Combination)


Game Concept Breakdown by Level


At first glance, levels 6 and 16 seem like they might be the most difficult. However, upon further examination, they simply require more concepts to be learned. That learning is not necessarily more difficult, there is just more of it.


Reviewing level 16 in game, it combines things learned about safe objects (Cubes), with a new dangerous object (Turrets). But each stage of the Turret tutorial slowly reveals new information about the Turrets in a relatively safe way.


Examining the method by which the player must learn something in level 16, it is clear that most of the things to be learned in level 16 are not very dangerous.


Conversely, we can assume that levels that require no new learning might be the most difficult. Revisiting the game, and recalling the more difficult test chambers, Level 18 comes to mind.



Level 18 requires no new concepts be learned, and only one concept is elaborated on. But it combines nearly all concepts learned so far in a set of compound puzzles.


Overall Progression vs. Difficulty

Applying the above perspective to all levels, this suggests that levels 1, 9, 13, 14, 15, 17, 18, and 23 might be the most difficult.



As shown above, the predicted level difficulties were accurate (ish) in about 80% of the cases. This is hard to judge accurately for a couple of reasons:


  1. I’ve played Portal a few times
  2. Level of difficulty is not binary


For others, using a scale like this may also prove difficult due to variation in game playing experience across genres, familiarity with the game being tested, and general tolerance level for challenge vs. frustration. There may also be difficulty in comparing results across individuals with disparate play experience and skill level.


Perceived Difficulty Factors

In the ratings above, the following elements were considered difficult:


  • Actual timing-sensitive sequences (e.g. fast switching portals to move an Energy Pellet)
  • Perceived timing-sensitive sequences (e.g. Boss Fight feels rushed even though there is loads of time)
  • Long combinations that must be repeated if failure occurs (e.g. Looping Portal Flings)
  • Sense of peril (e.g. Some late-game Turret encounters)




Portal is a game that feels good, and feels like it has a good progression. It feels challenging, but not frustrating. This progression/learning model is assumed to be effective because I like it, so breaking down the model into its structure and parts as rules to form a guide is a useful exercise. Applying these rules and structure to make a new systems-driven puzzle game seems sound (Note: In the sense of high-level design, not necessarily to make another game like Portal).


Applying this model to other games I like may help validate the model or identify common structures that can revise the model and improve the methods by which a new game is designed.



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