Sega has released Sonic CD on iOS and Android. If you haven't played Sonic CD and are a Sonic fan, this is a must download. Sonic CD was originally released on the Sega CD and is often heralded as the best game for the system, with some claiming its also the best Sonic game in the series as well. Its a spectacular display of 2D playforming that plays surprisingly well on touchscreen controls.
There have been a few additions too. Noticable right away is a widescreen view, which gives a much better view of whats coming up onscreen. There's also leaderboards and achievements for the online generation.