Anticlimax Boss: The final boss is just Eggman in his normal vehicle with four panels that flip around and whatnot. It's a case of dodging predictable attacks and waiting for a chance to hit him, or just taking the hit and then damaging him using invincibility frames (especially on his first hit, where it's legitimately difficult to find an opening). It's not overly hard or very exciting, especially compared to the final bosses of Sonic 2 or Sonic 3 & Knuckles, although it is a step up from the final boss of Sonic 1. On top of that, in the American version, the boss music is barely different to the normal one; at least the Japanese/European versions had a proper final boss theme.
Awesome Art: The cleaner, higher resolution look of the CD layout and expanded color palette has barely aged the game visually. The sprites are also much sharper, and then there's the OVA sequences...
Depending on the region, gamers were treated to one of two different soundtracks, each kick-ass in its own way (as expected from this series). The Japanese soundtrack,note also used in the original European release composed by Naofumi Hataya and Masafumi Ogata, has that familiar Sonic sound with a dash of J-pop complete with bits and pieces of sampling (notably, Xavier's "Work That Sucker to Death" is used for the boss music); while the American soundtrack, composed by Spencer Nilsen and David J. Young, is more atmospheric and rock-oriented. The past tracks in the U.S. release were unchanged due to technical reasons, which can be slightly jarring.
For whatever reason, the U.S. release lacks a proper final boss theme. It does differ slightly from the standard boss tune, with a few additional instruments and a couple of the sounds, like the sped-up Eggman laugh, at different points in the track, but you have to really listen out for them.
The soundtrack varies per version and region. North America never got the Hataya soundtrack prior to the 2011 re-release; Japan, of course, always had only their own soundtrack (Japanese fans probably aren't even aware there is a different soundtrack, at least until one song from the U.S. soundtrack was remixed for Sonic Generations); Europe got the Hataya soundtrack on the Mega CD version, but the Nilsen soundtrack on the Gems Collection version. The PC version has Nilsen's soundtrack in all regions. The 2011 re-release ultimately fix these woes by having both soundtracks selectable in all regions. However, the intro music for the Japanese soundtrack had the lyrics cut, presumably due to contract issues with the people who sang it. Fortunately, "Sonic Boom" is 100% unchanged. The remake even has proper looping programming for all songs so there's no awkward CD Audio fade-outs, and many of the US songs make use of some additional sections from their extended versions on the little-known "Sonic Boom" soundtrack CD.
Best Level Ever: Stardust Speedway, which allows for speedy movement in contrast to the other stages, which are, for the most part, mazelike and slow-paced. It also contains the race against Metal Sonic. It's so well-remembered among fans of the game that it made a reappearance in Sonic Mania, Metal Sonic included.
The American soundtrack vs. the Japanese soundtrack, in terms of "superiority". Flame Wars are not uncommon. This is a particular Berserk Button for Europeans, especially the Brits, who just tend to get whichever region is convenient. They originally got the Japanese soundtrack, yet when both the PC version and Gems Collection came out, the port was based off the PC version which was region-locked to the US, and since the Gems version used the PC port, all countries with that game got the soundtrack. Many a European gamer were not happy about the sudden change.
The level design is a big point of contention. Some like the increased focus on platforming and exploration, while others dislike the decreased speed and labyrinthine level layouts.
The boss music from the Japanese and European versions of the original as well as the Japanese soundtrack option in the 2011 version, which is available in the 2011 version in all regions. "Come on, now! Work that sucker to death!" This is especially in contrast to the nightmarish boss music from the American version.
The JP version of the Stardust Speedway Bad Future theme and its HURHUEHUEHUEing. Even more so in the funkier Generations remix.
Any of the Stardust Speedway music tracks, in both versions.
The American version of Palm Tree Panic, not to mention Wacky Workbench.
Franchise Original Sin: Sonic's first encounter with time travel, the slower paced gameplay, and overly large levels are problems that would be exaggerated in some of the later installments.
Funny Moments: The end to the Stardust Speedway race between Sonic and Metal Sonic. The former just barely makes it under a wall as it closes, leaving the doppelgänger to run headfirst into it and mimic Sonic's death animation.
Game-Breaker: Tails in the 2011 re-release. Not unlike his Sonic 3 & Knuckles appearance, Tails' flying ability allows him to simply fly over portions of some levels entirely, the game lacking any upper ceiling boundaries to counter this. Because of this, the game prevents the player from attaining achievements/trophies when playing as Tails.
Goddamned Boss: Collision Chaos' boss. All you have to do to beat it is to reach the top of the pinball table, but you might take a lot of time trying to do that, as the flipper's controls are very strange (there is a minuscule delay and the physics are off). Robotnik/Eggman will also throw a lot of bombs that act like bumpers, to keep Sonic from reaching him.
Debug doesn't work in Time Attack mode. Though it seems to prevent the player from cheating, there is a different bug that will give the player a "00:00:00" time record after the level is completed. This way, the player can easily unlock the game's extra content.
As shown in this video, it's possible to warp from the beginning of Collision Chaos Zone 1 to the end if Sonic has the power sneakers.
In the 2011 version, at least in the Windows Steam version, sometimes Sonic will go through the ceiling. Unlike the Genesis games, though, a restart is not necessary; jumping enough times will get you on top of the level, where running right a certain amount will trigger the goal even though it can't be seen from there.
Heartwarming Moments: Even though Amy is Sonic's Stalker With a Crush, Sonic is still willing to save her when Metal Sonic kidnaps her. And keep in mind, this game is Sonic and Amy's first meeting. By all accounts, Sonic saved a complete stranger who was enamored with him to the point of childish obsession without any hesitation. No wonder Amy likes him so much...
One line of "Sonic ~ You Can Do Anything" is "Excalibar - It's not that far". In Sonic and the Black Knight, Sonic gets Excalibur. Looks like it wasn't that far after all. Another line from the same song is "Doom room, cosmic zoom, heads up Jake it's Sonic Boom!". "Doom room" becomes only more hilarious when you consider the Barrel of Doom from Carnival Night in Sonic 3.
Hype Backlash: Back when Sonic CD was rarer and harder to find, the game was considered one of, if not the best game in the series as a whole by those who played it. However, when re-releases and even a remake allowed it to become accessible, the game became more divisive, with some believing that the game didn't live up to the hype. As a result, the game has become more divisive over time, though few seem to outright hate it.
It's Easy, So It Sucks: Aside from the music, the biggest complaint leveled at this game is that the Eggman boss fights are too easy. None of his machines take more than four hits to destroy; most take three, Tidal Tempest technically only takes one, once you get past his defenses, and the Quartz Quadrant and Stardust Speedway battles don't have you attack him directly at all. Bosses in other classic Sonic games almost always required eight hits to beat (mini-bosses took fewer hits to kill and final bosses usually took more).
Just Here for Godzilla: When Sonic CD was re-released on Sonic Gems Collection, many fans bought it just for this game alone.
Some of the JP music, like the Stardust Speedway and boss themes, can be kind of silly, but no less catchy.
The robotic voice in the Japanese bad future music for Metallic Madness sounds like Microsoft Sam and is basically saying the opposite of the lyrics of that version's theme song, but the song in general (especially the instrumentation) doesn't refrain from reminding you that you screwed up.
"You can't do anything, so don't even try. Get some help. Don't do what Sonic does."
Nightmare Retardant: The Bad Futures may look quite bleak, but at least you have the comically ineffectual Badniks. A Kumo-Kumo, for example, will jump into the air and shoot spider webbing at Sonic to restrict his movements, but the broken-down Kumo-Kumos in Quartz Quadrant's Bad Future will just jump up and down pointlessly. Taking the cake, however, is the Taga-Taga. A normal-functioning one will come over to Sonic and launch its spikes. The ones in Tidal Tempest's Bad Future, on the other hand, will retreat upon catching sight of Sonic.
Older Than They Think: While it's more commonly known nowadays, some fans were, and still are, unaware this game marked Amy's first appearance, making her as old, or perhaps older than Tails.
Polished Port: The XBLA/PSN/iOS/Windows Phone 7 ports. As they were built from the ground up from a fan-made engine, it's closely based on the original Mega/Sega CD version, rather than being based on the PC port, has HD true widescreen support,note As in, it's not lazily stretched or cropped, but truly extended picture for Widescreen TV screens. Tails is an unlockable playable character, and it even has the option to use the traditional spin dash from Sonic 2 onwards instead of the standard one. There's also an option to switch between the Japanese and American soundtracks. The only gripe is that due to licensing issues, the JP/EU opening and ending themesnote "Sonic - You Can Do Anything" and "Cosmic Eternity - Believe in Yourself" were replaced with instrumental covers.
Porting Disaster: While not horrendous, the Gems Collection port suffers slightly due to being ported from the early PC version. It is lacking a few graphical effects such as fade out (which were excusable in the PC port as it was meant to help it run on lower end PCs too but had no place still occurring on much more powerful hardware), the debug mode doesn't work properly due to the controls not being remapped and the music transitions are edited only according to the U.S. release (meaning Metal Sonic will play the "G" future remix if you achieve it). The port was not edited for the PAL version either, meaning they got the U.S. soundtrack rather than the Japanese one they had for the original release.
Scrappy Mechanic: Time travel posts can be used up without activating them if you build up speed for long enough to generate sparks and then lose your speed, or if you cross another time travel post. Since you're running at full speed in an attempt to activate the time travel, you'll need to memorize or stake out the path you're going to take, or put up with the risk of walls, enemies, and other posts getting in the way and ruining the attempt. Very frustrating if you're trying to find Past posts so you can get Good Futures.
Signature Scene: It's very hard to talk about the game without mentioning the Metal Sonic race.
Suspiciously Similar Song: The American boss theme sounds a lot like "Pressure Road" from Ys II. The resemblance is one thing, but they both have the distinction of being nightmarish, cacophonous, and incredibly out of place in series that usually have upbeat music.
Much of the American soundtrack, despite its reputation. Having a playlist of the soundtrack, or better yet the officially extended CD. Nearly the whole soundtrack is ambient folk crossed with alternative rock and extensive vocal harmonies, making it very soothing to listen to as a stand-alone product.
Good Futures. No enemies, a bright and colorful soundtrack, animals living peacefully, and technology being used to benefit nature instead of harming it. One of the earliest examples of Solar Punk.
Hearing "Sonic Boom" play during the credit crawl.
That One Achievement: Savior of the Planet. Getting the Time Stones makes getting the achievement/trophy impossible unless you get the last Time Stone in Metallic Madness Zone 2. Also qualifies as a Guide Dang It! for most fans.
That One Boss: Metal Sonic for some. There's a lot of obstacles in the way, not to mention awkward jump timing, and if you miss any of these, the quirky physics of the game will slow you right down, meaning you need to have near-perfect platforming if you want to keep up with him.
Wacky Workbench, thanks to the bouncy bottom floor. When it comes to getting a good future in Zone 1, it's even harder because of how complicated the path to it is, though at least it's easier to do in Zone 2. It also contains That One Boss. It is given a Shout-Out in Sonic Advance. The electrical coils in the upper areas of the level are also problematic (as, combined with the bouncy floor, you can be thrown into the top of the stage right in time to end up in front of an active electric coil; plus they look like they're part of the background, which can be disorienting).
The Special Stages. Especially the 7th one.
For players trying to finish Time Attack mode in under 25 minutes, Metallic Madness Zones 2 and 3 are easily more irritating than the other levels. Zone 2 takes much practice to complete in under three minutes, as opposed to the previous non-boss levels, which can be beaten in under one minute (and in exceptional cases, 30-45 seconds). Zone 3 has a Platform Hell section at the start, and three extremely tricky enemies to defeat before reaching the boss. You'll be lucky to finish it within two minutes, like the other boss levels.
They Changed It, Now It Sucks: The American soundtrack got a lot of flak just for replacing the Japanese soundtrack. This mentality even extended to game critics such as GameFan Magazine, which rated the American version 30% less than the Japanese version for this very reason.note They gave the Japanese version a perfect score of 100%.
Visual Effects of Awesome: The 2011 remake's Special Stages have had their framerate considerably improved, giving them a very fluid panning effect as you rotate the camera behind Sonic. It also helped improve the playability of these stages (as depth and perspective were sometimes difficult to judge due to the lack of smooth motion).
WTH, Costuming Department?: As this is one of her few pre-Adventure appearances, Amy sports her more tomboyish, spikier look that just seems weird.