Story makes no sense except with respect to a fistful of specific paths. Character development and plot flow are very inconsistent (-2). Scenarios between different levels may not be relevant to one another, undermining any sense of dramatic tension until the very last stages; tension is undermined further with consecutive playthroughs as the player realizes that the grid is completely arbitrary in its arrangement (-1). The story is only completed when every level has been played and the "real" ending scenario is unlocked, completely undermining all the other "fake" endings from the main game and any sense that any of those events actually mattered (-1). At the very least the narrative choice system reinforces the game's themes surrounding Shadow's internal struggle (+1), giving players the chance to explore it for themselves.
Final Score: -3. Shadow's Narrative Choice system actively harms its narrative.
Choices affect which levels the player visits and are made by selecting one of three potential goals for completing each level. These goals are not consistent between levels, however, and can range from "kill all enemies of one type" to "find all the switches and activate them." Many of these goals can change what would be a straightforward five-minute level to a frustrating twenty-minute scavenger hunt in a looping stage for that one tiny bat the player didn't kill, making the game's overall pacing very inconsistent (-1) and possibly discouraging the player from making particular narrative choices that they ordinarily would want to make based on the relative difficulty of the goals presented (-1).
Final Score: -2. The narrative choice system in Shadow the Hedgehog offers players the choice of either having gameplay impose decisions on them or of having their decisions impose heavily on the pacing of the game.
Player's choices essentially don't matter as the same ending scenario can be accessed through multiple, completely different paths. If the player goes evil for one level, then goes completely good, that one evil choice will more or less be completely forgotten, without so much as a minor manifestation of consequences (-1), meaning that an hour into the game players will completely forget their choice as well. There's absolutely no sense that the other characters are acting on this story or reacting to the player's input in any way (-1); if the player helps the aliens in one level, Sonic won't care three levels down the line as choosing to help him still has to be an option, and vice-versa.
Because levels aren't necessarily in a logical progression, characters and entire plots may in fact disappear, creating confusion as to the player's preferences but not necessarily ambiguity (-1), as they can be nursing a friendship with a specific character or faction only to have it suddenly be gone for an entire level with no further reference. The recency effect takes hold as players are more likely to make choices based on what they've seen in the last cutscene and how they interpret the identity that's been built for them up until now (+1), but this is extremely tenuous.
Final score: -3. Shadow the Hedgehog is so married to a specific scheme of choice that it completely disallows the manifestation of consequences, and the lack of logic to the game's narrative progression actively harms its discernability.
Players don't necessarily get the sense that they're building Shadow's identity so much as choosing paths. Shadow makes the real decisions entirely on his own depending on what levels the player moves through, leading to arbitrary conclusions that players wouldn't necessarily draw on their own (-1). Relationships with other characters are nonexistent as they do not respond to Shadow's choices (-1). Enemies of one faction or another will attack Shadow whether he's helping them or not, and there are no rewards or penalties from either side or any of the ancillary characters one way or another.
As said before, the progression of stages/cutscenes does influence the way the player perceives Shadow (+1), which can influence their own choices and make them feel like they're doing something, and the game does build a new narrative for each playthrough (+1), even if it doesn't make sense. However, as cited in the Narrative Integrity section, there is a canonical "real" ending that the player unlocks from completing all the different paths available in the game, completely undermining any sense that the player's participation matters in this story (-1).
Final score: -1. Players make choices that affect the outcome of the game, just not in any logical fashion.
Metascore for the PS2 version of the game: 45 (-2).
Most reviews cite that the choice system is a neat addition, but poorly executed due to lack of response in-game; IE, opponents from either side will always attack Shadow whether he's helped them or not (-1).
Final score: -3.
-2.4 -- Shadow features an extremely harmful narrative choice system, owing most of its problems to a lack of discernability and a highly inconsistent narrative.