I don't wanna be the guy defending sonic 06... I aknowledge that it was a terrible game, but I don't know. Some of the stages were jst really excellent. It started the same with me. I bought the game, hated it and got saints row instead the first time, which was a great decision. Than I found it somewhere for 5 euro and bought it again just to "own" one of the many sonic games I have.
The new xbox dashboard was out and the new install feature was now there. Installing the game did reduce a bit of the loading times and I decided to finish the game.
I found out that it did have some good stuff. Basically everything about the game sucks imo, except for what they were aiming for with the way sonic stages should be done in 3d. Speed and action/platforming were balanced. It sucked that the game was a total unfinished mess. Even if it were fnished, a lot of the decisions they made by making the world realistic, having the worst story line in a sonic game ever and the hub worlds would still make it an average package. I think finishing the game got me used to the crappy controls and made me see some positive light :S. I really love some of the stages and sometime I wished that the game would be redone but done right. But I guess that's too late
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Anyway, selling your 360 ain't really a bad decision. The 360 has a great library of games, but it seems ps3 gonna shit on 360 this year. It just shows that PS3 even though it had a slow start, are always about quality games. Even though in the early days I used to hate ps because of sega still being in the console business, I can aknowledge now after playing lots of ps games, that sony really has a lot in common with SEGA. Originality and quality games. I recently got a ps3 and I don't even use my 360 anymore. SEGA games like valkyria and yakuza totally won me over, but also sony games like infamous, killzone and resistance and alot more. I recently bought MvC 3 for the ps3 and the ps3 controller is so much better for fighting games.
The only reason i'm keaping my 360 is because I don't really ever sell my stuff, knowing that I might regret when something awesome comes out. I guess you should think about it. If your desperate about cash, than go for it. If you got it well, i'd say why not keep it.