The game is a faithful recreation of the classic Sega Genesis title, but adds a secret zone called the Hidden Palace that was removed from the original game. The game was made by the same team that released the Sonic CD iOS-port previously. Our sister-site TouchArcade has more:
Just a quick heads-up to let you know that the Sonic The Hedgehog 2 [$2.99] remastered update, which we gave you some first impressions of yesterday, is now available as a free update to the original game in the App Store. In addition to improved visuals, widescreen and Universal iPad support, and a 60fps frame rate, this remastered Sonic 2 also includes brand new additions like a Boss Attack Mode, an online 2-player mode, Knuckles as a playable character right from the start, and the first ever official inclusion of the long-lost Hidden Palace Zone which was scrapped from the original Sega Genesis version of the game just days before release back in 1992.
Sonic the Hedgehog 2 is available for $2.99 from the App Store for iPhone and iPad. [Direct Link]