In sad news, Sonic Team has no plans to continue Sonic 4 after the release of Episode II later this year. After delays and an uneven reception, Episode I of Sonic 4 was still a nostalgic return to a damaged franchise.
Speaking to Digital Spy, Sonic Team's producer Takashi Iizuka said this about their future plans:
"We are looking forward to hearing the feedback from the users for Episode 2, but we are currently not planning to release another episode. We just want to see how the users accept this episode."
Fortunately, Sonic 4 Episode I was received very well commercially, so perhaps this decision is based more upon Sonic Team's opinion of the episodic format than on the game's success. Due to Episode I's profits, Episode II is said to be receving extra development time. Sonic Team is providing new zones and new enemies, but will also bring back Tails and Metal Sonic.
Here's to hoping Sonic will move on to bigger and better things after Episode II.