I just finished Sonic CD on Android. I have been a huge Sonic fan ever since I was four years old. I had been wanting to play this game for quite some time, but I have a migraine problem because of which I am unable to play mobile games which have a virtual gamepad. This time however, I was determined to try this for once and get over my pain to see what happens. I did manage to beat this game with a bad ending, and although my head hurt a lot, I am now proud to say that I have played every single classic Sonic game in existence.
This game is probably the only evidence that Sonic is faster than The Flash, as we need to build up speed if we have to travel to the past or future. It is a bit difficult though, since there are so many obstacles coming in your way when you are on higher levels. One thing I really find annoying in classic Sonic games is that the game wants us to run fast, and then punishes us for doing the same. The touchscreen of the phone was also very unresponsive and that caused me to lose unnecessarily more number of times than I'd be willing to admit.
Sonic CD is something of a case study for SEGA developers. It does not have any customisable characters, or even a lot of characters for that matter. It introduced two characters who have now become a major part of Sonic's lore. The cutscenes, the quality - everything about this game is perfect. If you're new to Sonic the Hedgehog, I'd recommend you to definitely try it once.