I feel like I have to say this, because I've been having frustrations with it lately in cleaning up some achievements, but even if I wasn't going for that, I still feel comfortable in saying that the final boss in Sonic Generations could possibly be the worst boss fight I've ever played. It's so unbelievably frustrating for you to gain all that distance to the bad guy but then get knocked back quite a way for you to have to regain that distance. Plus you're on a timer because the number of rings you have count down all the while. Plus the controls are just terrible, you never ever feel like you're in control. On top of it all the music's terrible and you play it hearing nothing but this all the while.
I think they're saying it's a homing shot? Can't be sure.
Some actual Sonic 4 : Episode 2 gameplay here. Been waiting long enough!