Sonic the Hedgehog 2006
A game meant to celebrate Sonic's 15th anniversary and is notorious for its bad reviews. You'd expect a game like this to have a lot of time and effort put into it, but there wasn't. The game has terrible controls, long load times, mixed opinions on voice actors, although most people complained about Jason Griffith. Even if those problems were fixed, the storyline is pretty bad, including an implied romance between Sonic, a hedgehog, and Elise, a human. Odd. They rushed this game to make it closer to the Holiday season, but they obviously should've worked on it more.
Sonic the Hedgehog 2006 is regarded by some as the worst Sonic game ever made.