The portal mechanic is very unique and innovative and works perfectly in a puzzle-platformer. It runs smoothly and is very easy for new players to understand. It is made clear to the player early on what type of surfaces can be applied with a portal and those which can't. An issue is that often it looks like a surface should be able to have a portal applied but it doesn't work which can lead to some frustration.

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The puzzle design flows well with new mechanics being introduced slowly over time such as Lasers, the Weighted Companion Cube or Turrets. The cube is the most interesting where it can be used to avoid environmental damage, solve physics-based puzzles and even have a personality applied to it. Each puzzle is memorable especially with the voice of GLADOS resonating through the halls of the abandoned testing range. Puzzles are easy to understand with clearly defined goals. Additionally, the game has a well designed achievement system which is excellent content in itself, something some games take for granted giving players achievements without reason instead of designing them to guide the player or have them complete difficult tasks.

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One of the biggest selling points of Portal is its charm from the snappy comment of GLADOS to the high-pitched songs of the turrets as they load the player full of bullets and much more. The charm of Portal is most definitely a high selling point, something which some games may underestimate and I'd argue that the personality of a game should be taken into account through design if resources are available.

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The biggest flaw of Portal is the length of the campaign and the low difficulty of puzzles. The main campaign is very short for a player of a higher skill level if they don't aim to complete every achievement the game has to offer. The balance of this is difficult to achieve within a puzzle game as puzzles which are too difficult may cause the player to completely quit the game.