Shadow the Hedgehog is terrible execution in technical and design mechanics that will foul anyone sonic purists outlook.
Its weak points begin to show evident in the story. The story in Shadow the Hedgehog, in its layout does not compliment the sheer idea of Shadow being an anti-hero and feels like it has been told in different shells many times before throughout the sonic series. Many times throughout the plot convenient contradictions are made to contradict plots from other sonic games. Not only is the story bad, it is not told right.
The voice acting in Shadow the Hedgehog sounds phony and sappy at best. For a character like Shadow you'd expect much higher tones of confusion, anger, and rebellion and although sometimes you'll find that in Shadow the Hedgehog, whenever it occurs it just sounds extremely weak.
Even if you just want to get some good gameplay out of this game, you will find that there's nothing to offer.
In this installment into the sonic franchise the in-game camera still has not been fixed, along with a very watery set of mission mechanics that are reminiscent of previous installments into the 3D side of the sonic franchise. The lack of mission components that award speed (during the mission) creates a notion that the best part of sonic games is all but forgotten, of which would be the sense of speed.
The sonic franchise has hope but the sonic team needs to deal with the problems that really matter.