Why was shadow the hedgehog game so bad

It wasn't 'bad' persay, as a stand-alone game it was okay, but as an addition to the Sonic franchise it was poorly received, mainly due to these issues:

-The use of guns was something a ton of fans disliked. No other Sonic character till that point had ever used handheld firing weapons.
-The near endless amount of possible ways to go through story mode because of the branching storylines was something a lot of people also disliked.
-A lot of people just thought that the plot itself and gameplay were bad.