Sonic CD is a massive improvement over the entry to the series two years prior. I appreciate the time travel mechanic a lot. It provides a fun amount of challenge in navigating the unique levels, which I must say have beautiful design, in order to get enough momentum and time to complete the warp, as well as burning off a time warp that you don't want to use yet. Searching for the robot generators is a nice incentive to stay in the levels in addition. Most of the levels offer a nice unique gimmick which makes them interesting and not too stale to navigate, and for the most part, isn't too challenging, but isn't a complete cakewalk either. The game is engaging on these fronts, which is a plus that Sonic 1 did not have. However, some negatives for CD include the god awful special stages, which due to hardware limitations, are much more tedious and painful than they should be, so much so that after getting one time stone, I just gave up on them entirely. The bosses, while more unique than Sonic 1, are way too easy at times. The opening and final bosses are pathetically piss easy, and honestly have no right to be in the game. Also, fuck Metallic Madness Act 2 royally. That might be the WORST level I have ever played in a Sonic game. In the end though, my overall opinion on the game isn't too dampened.