I think everyone is now aware of the bad ratings this game has got but I do think some of the people who've rated it have only played it for 20 minutes or so before judging it. Yes it has some obvious faults but having played it from beginning to end, I found it very addictive stuff and I've played it consistently for weeks.
The game is split into 3 types of gameplay; town sections where you wonder around Soleanna, action stages which is the main part of the game and speed stages where Sonic runs at full pelt through a level avoiding obstacles. I think the main criticism of this game is that the town and speed sections are poorly executed, the town sections in particular suffering quite atrocious slowdown with poor loading times. However get to any of the action stages (which is the real meat of the game) and things improve considerably. While not flawless, these levels are extremely good fun and as each one is unlocked, it can be returned to again so secret routes and stuff can be discovered. This for me is where the game really proved addictive and as such, I've rated it 3 stars despite the obvious flaws that it has. After all, surely the point of a game is to entertain and be fun?
So to summarise, you may well hate this game (a lot of the reviews here prove people do) but to anyone who enjoyed Sonic Adventure 1 & 2, you might well find plenty to enjoy here so play it for yourself and form your own opinion.