Games that have made you sad.

[Bolt the Cat]

The mechanics that are "promoting speed" aren't any good though.

Explain. Simply saying they're "not any good" is subjective.

Not only that, they belong in racing and normal platforming games, not Sonic. So by your logic it's still a bad game.

Sonic is a platformer, though, and racing elements are conducive to speed, so no, by that logic they still fit.

As your logic follows, Metal Gear Rising is a terrible game (despite not being out yet), because it includes mechanics that aren't conducive to a stealth game.

Well IDK anything about Metal Gear gameplay, but generally yes. There are exceptions to the rule, however, such as if the game is a spinoff or reboot, but the examples that have been listed so far are neither.