Sonic the Hedgehog (1991 video game)/YMMV

The original Sega Genesis game:

 * Breather Level: Star Light Zone's greatest hazard is the long gaps and the sparce checkpoints, but there isn't much else to complain about compared to its preceding level Labyrinth Zone.
 * Goddamned Bats:
 * The Roller enemies in Spring Yard Zone, which move incredibly fast and appear quickly.
 * Burrowbots in Labyrinth Zone and Act 3 of Scrap Brain Zone are hidden in the ground except for their drill noses, so an impatient player may easily get blindsided by them as they leap into the air.
 * Goddamned Boss:
 * The Labyrinth Zone boss can be quite intense, given it's heavily dependent upon timing - both in your jumps and the movement of spears emerging from the walls - and how much air Sonic has left, in addition to having to chase Eggman up through an incredibly small pathway. It's this, along with the overall difficulty of the zone, that contributed to the rearrangement of the stages.
 * The final fight has you playing a round of whack-a-mole against Eggman. Two out of four pistons will move and you must guess which one the doctor is hiding in. It can be quite troublesome when doing a speedrun, especially when the two middle pistons pattern comes up.
 * Good Bad Bugs:
 * In the original version, once you finished a level, if you were airborne while offscreen as the "level complete" score tallies came up, the game wouldn't take control away from you. This not only means you can continually jump past the goal post to rack up bonus points, you can also jump back into a bonus ring you may have accidentally missed.
 * Some of the physics glitches in the infamous Game Boy Advance port Sonic the Hedgehog Genesis can be exploited. In particular, if Sonic gets on top of one of the "R" bumpers in the Special Stages, then the stage will rock back and forth endlessly, which can be useful for getting your bearings.
 * In the 2013 remake, it's possible to get Knuckles and Tails together via glitching.
 * Most Annoying Sound: The "Ding-ding" chimes as your air supply depletes underwater.
 * Scrappy Mechanic: The "spike bug" for those used to playing the sequels and later versions of the game, which lack this behavior.
 * Signature Scene: Sonic popping up and finger wagging while smirking at the player in the title screen, and the entirety of Green Hill Zone, are the series most iconic elements by far.
 * Suspiciously Similar Song:
 * Marble Zone is "Music to Watch Girls By" lifted nearly note for note.
 * The Spring Yard Zone theme sounds an awful lot like "Every Little Step" by Bobby Brown.
 * The Final Zone theme sounds similar to Duran Duran's "Planet Earth".
 * That One Level:
 * Marble Zone is disliked for being a massive pacebreaker following up the fast and speedy Green Hill Zone. Plus, the number of booby traps, lava and crushers can make navigating it difficult, especially for the impatient.
 * Labyrinth Zone. It's a water level, which means you're playing as a slow Sonic in constant danger of drowning for most of it. Then there's the Goddamned Bats in the form of Burrowbots and Orbinauts that can make life miserable, especially if you had the misfortune of failing to get all the Chaos Emeralds beforehand. To top it off, it ends with That One Boss. Oh, and it's also your introduction to one of the most infamously terrifying pieces of music in the series, and since it plays when you're about to drown, you're gonna be hearing it a lot in this tough water level. What fun!
 * Scrap Brain Zone Act 3 is a Palette Swap of Labyrinth Zone, so all the problems with that level are present and accounted for. In fact, it's even tougher because the air bubble pockets are more spread out, and you have to wait longer for the bubbles to come out. It's also a Marathon Level unless you take the shortcut at the start, which makes it almost a non-issue.
 * Special Stage 3 can be this, since while it's easy to reach the Chaos Emerald in one fell swoop, it's just as easy to rocket straight into Goal blocks, potentially with unwanted assistance from bumpers.
 * What Do You Mean, It Wasn't Made on Drugs?: The psychedelic backgrounds of the Special Stages.

The Game Gear/Master System game:

 * Polished Port: The Sega Game Gear port has a more cramped screen than the Master System version, but much of the level design and boss fights as well as Sonic's sprites are redesigned to alleviate this, making the game much more forgiving in difficulty, especially in regards to Jungle Zone Act 2 and that zones boss, and getting the Chaos Emerald in Labyrinth Zone Act 2.
 * That One Level: Jungle Zone Act 2 in the Master System version. Unlike the Game Gear port, the vertical oriented stage is subject to Ratchet Scrolling, which forces you to be very careful with your platforming since one slip up can mean falling to your death.

Both the Genesis and Master System/Game Gear game:

 * Anticlimax Boss: The final boss for both games. In the Genesis game's case, it is a fairly challenging, if tedious, final boss, and the lack of rings doesn't help, but it's not a particularly exciting battle: you're just locked in a room where Eggman tries to crush you to death with pistons, and then sends electric sparks flying after you. The Game Gear final boss is insultingly easy and pedestrian, where Eggman's weak spot is out in the open, and he has no recovery time for his collision damage, with your only threat being your lack of rings, and an easy to dodge combo of floor-mounted flamethrowers and the occasional electric spark flying down at you... he can literally be beaten in less than 30 seconds (this is not the case with the Master System version, which replaces the flamethrowers with an electrified wall and is much harder to beat). Fortunately, the Genesis version lets you deliver a final blow to Eggman while he's escaping with just the right timing.
 * Suspiciously Similar Song: The Scrap Brain Zone's theme in the 16-Bit version sounds reminiscent of the Blade Runner theme, even featuring gloriously synthesized Timpani. Meanwhile, the Scrap Brain Zone theme in the 8-Bit version sounds like a Suspiciously Similar Song of the zone's theme from its 16-Bit counterpart.