It's a shame this was something of an obscure title for a while due to the relative unpopularity of the Sega CD add-on. This is a really cool game! The time travel concept was a neat innovation, and it made for a unique way of traversing the different stages as you searched for ways to travel to and from the past. It also introduced one of the iconic villains of the series in Metal Sonic, adding him to one of the coolest stages in 2D Sonic games. The real star of the show is the soundtrack, however. I do prefer the Japanese OST to the US one, but I think both produced some memorable tracks in Sonic's musical library.