The whole trouble with Sonic Unleashed was it was released 6 months before it was ready to ship, to meet the silly Christmas period
That sure sounds familiar...
Difference is 06 could have been average/mediocore, while Unleashed could have been even bettter and more accessible round the masses.
The Real problem with Unleashed lies around it's structure. They handeled the Werehog the worst they possibly could, making you play 2 stages in a row sometimes, making it mandatory to look in every corner in the Levels to collect Medals to progress through the game, and a slow Level-up system, were a detriment.
It should have been no manadatory Medal Grinding and either:
Making Werehog a seperate sort of Storyline sort of speak/more more freedom to choose Hedgehog/Werehog stages, similar to SA1,06 and JOD.
Or/and have all/most Moves unlocked from the start, to make it more fun from the get go.
Oh and remove the Battle Music.
Simple desicions like that, would have made Unleashed at least in the 70's on Metacritic, and woudn't be regarded as a "bad" Sonic game.