I could never begin to describe why Shadow's own game is the biggest sinker in the Sonic The Hedgehog franchise.
I could go over everything of what makes this game truly so awful, but I'll just mention the most overlooked issue, the Story.
When Shadow The Hedgehog was advertised, you were asked one question "Hero or Renegade" effectively meaning that Shadow's own game was going to be getting a morality system, despite the fact that he had already proven himself an Anti Hero at best in Heroes, and that he just flat out hates Evil, even in his debut.
Here, you have the opportunity to perform heroic tasks, such as helping Sonic & his friends (who don't help you, if I might add). Or by performing nefarious deeds for the overly generic villain, Black Doom.
Want to know why this premise is so pointless?, it's simple...
There are a total of 10 non canon endings, all of which are unlocked by setting out on a morality specific pathway to get to said endings. The biggest problem with these, is that they're all poorly handled, poorly written, and are just the same situation, in the same place, with slightly different dialogue.
So, 10 half assed endings, all of which aren't much different from the other, sucks.
Want to know what the worst part is?. After unlocking all of these endings, you are given a Last Story Segment. The worst part of this?, it's canon to the Sonic The Hedgehog Universe. Not only does this wipe out the whole point of the game, but it's also just as bad in terms of what it accomplishes.
In the Last Story, Shadow ends up saving the day anyway, along with having a plot point that would of ultimately destroyed Black Doom and his Comet anyway, again making the whole morality system meaningless, because of the fact that there was always a plan to destroy Black Doom, even without Shadow.
All in all, a completely unremarkable Story, with tons of plot holes, cringe worthy dialogue, all whilst having cringe worthy notions of a menacing threat at hand for a Sonic game, effectively forcing edginess in the worst possible way. And 10 different endings all of which are very similar to each other, whilst not giving the player what they were supposed to be given.
A Morality System that could determine an interesting outcome, without something to overshadow it completely. (Pun intended)
Easily one of the worst stories present in a Sonic game, along with being the worst game out there. The game doesn't even qualify for the "So Bad It's Good" category, it's just plain awful.