FWIW, Unleashed gave the player full camera control and it's the last Sonic game to do so to date. Colours, Generations, Lost World and Forces all remove camera control, but before Forces it wasn't so that they could only render half levels. Colours was limited by the Wii control scheme, and it was a common thing not to have an disparities between control schemes. Generations is where things get messy. I just made a post about camera and warping effects that were used in Unleashed over in the "fastest game" thread. Camera control really tore those effects apart, but it wasn't the biggest thing. All of the boost games rely heavily on making Sonic follow scripted paths. Even at times when you don't realise it, Sonic is bound to invisible splines that make him weave around corners and generally just follow the route without pressing anything other than up on the analogue stick. But this gets absolutely broken when you rotate the camera. The up direction will still make Sonic follow the path forwards and down will have him go the opposite direction, even if the camera is side on to Sonic. You can still get this to happen quite easily in Generations by running around against walls and forcing the camera to turn a little on its own. Camera control was removed from Generations simply because it it didn't work with the game and the developers weren't willing to make a proper fix. And with Lost World it was probably just not a good fit for the level design. But Forces... They took full advantage of being lazy.