If you're a Sonic fan, then this will be familiar. Sonic CD plays like its Genesis era counterparts. But what made the game so unique, and cool, was the time travel "gimmick." In each level there are multiple gates you can pass that will allow you to travel forwards or backwards in time, utilizing the Back to the Future method of time travel (go fast!). Depending on when in time you are the levels change with different layouts and enemies. There are basically three levels in one for ever act in the game, and playing right can change the ending of the game (a novel concept for a Sonic game in the early 90s).
The unique levels are largely the reason Sonic CD stands out after all these years. Well, that and the cool way the game changes perspective that blew us away in the days before we knew what Sonic looked like from above. I'm not going to review Sonic CD as a concept though, it's already been lauded by us, and many other outlets, as one of the best 2D platformers ever. So what's new and interesting about this port?
For the port, Sonic CD is presented with multiple filters (though I prefer the one that keeps it nice and pixelated), and full widescreen support. The game looks great in HD, and the colors are vibrant, accenting the changes in time periods. The controls are still tight in most places, and annoyingly less tight in the special stages.
A time attack mode and leaderboards bring Sonic into this generation, and offer a humbling experience to those of us who thought we were fast. Extras and bonuses like getting the option to switch between the Japanese or US soundtracks add to the package. But cooler than all that is the inclusion of Tails in Sonic CD. After beating the game, you unlock Sonics two-tailed foxy friend and can run (and fly) through the game again as him.