Sonic CD is a 2D platformer that has you as a hedgehog finding your way through labyrinth like levels. Between getting from the start to the finish of the level, Sonic can collect rings. These rings are insurance. If you get hit with rings, they all spray out of the hedgehog. If you get hit without any rings, Sonic dies and its back to the last checkpoint. If you have 50 rings at the end of the level, you can jump up into a giant ring that lets you do a bonus stage for a chance to get a chaos emerald. The bonus stage feels like Sega's version of Sonic running around a Mario Kart track. After every 2 levels comes a boss level that has you stock up on rings or lives before you face the boss Robotnik. The game breezed by in a few hours without me noticing.
For those that haven't played any Sonic games from the 90s, the controls are simple enough to use one button. That one button is jump if you're standing or running. If you're ducking and push the button it charges up a spinball. When you release the down direction, Sonic will fire off with a super boost of speed. If you press down while running, Sonic tucks into a ball that will damage enemies.
The real gimmick of Sonic CD is the ability to go into the past or future. You do this by first hitting a sign and then going so fast that you will either go to the era. It feels like nothing more than a pallet swap. There are changes here and there, but you won't need to visit one era or another to progress. Plus there is a screen that takes Sonic to the era and it stops the gameplay. There's not that much variety in gameplay. Even the brief water levels only slow down Sonic, forcing you to find air bubbles to breathe. He can't swim or anything.
For the explorers out there, jumping between past, present and future will reveal secrets. Visit the past to improve the future. When you make two levels have good futures, the third level will take place in the good future. Without the exploration, every level goes by after a few minutes.
New to the series is a Metal Sonic who kidnaps Amy shortly into the game. At some point you will need to race Metal Sonic to get her back. It adds to the unique boss fights. The boss battles are what make the game stand out from other old school Sonic games. You need to defeat each Robotnik boss in different ways other than the traditional 'hit him.' Some you'll need to run fast while dodging objects. Others you'll need to go up on hovering rocks and still others involve chasing him.
Since the game came out between Sonic 2 and 3 there are only a few items to find in boxes. Items like extra lives, 10 extra rings, super fast shoes, temporary invincibility and a shield barrier that lets Sonic take an extra hit. There is nothing new that you won't find in the first two Sonic games.
Unique to the Sonic CD is an animated cartoon introduction and then another when you beat the game, before and as credits roll. Both are nice to look at and pretty brief. They add some much needed flair outside the game to make it feel different from the other old school Sonic games. Sonic CD shouldn't take more than 3 hours to complete. Once you complete the game, it unlocks Tails as a playable character. Tails is a fox that plays the same as Sonic, but if you tap the jump button in mid air, Tails can helicopter around for a while. I can understand why he is an unlockable character, because with him it becomes far too easy to just hover over entire levels.
The game feels easy up until a point, which lets new players get far into the game before it gets challenging. To add to how easy the game is, if you use all your lives, you start at the same level you were at, instead of restarting the zone. The backgrounds are beautiful and have a lot going on. The levels feel large enough to get lost in. The real challenge is traversal, because the enemies are quite forgettable. Sonic will be bouncing off of springs, doing loops, running up ramps, zooming through tubes, running against treadmills, avoiding crushing blocks, hopping on enemies, running around what I can only call gears, but they're not and much more. It didn't feel to me like there were many moments for Sonic to get up to top speed.
Even with the future and past dynamic, the game feels like a big sidestep from Sonic 2. There is nothing new here, but is that a bad thing?