These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Sonic Adventure
Anti-Climax Boss: Both Amy's and Big's final boss can be beaten in under 30 seconds.
The bosses with playable characters, along with the first few E-Series battles have particularly slow AI and can be defeated before they even so much as make a proper attack.
Best Level Ever: Consensus seems to be Speed Highway, the fastest-paced Sonic level in the game. Sega appears to be part of the consensus, as they practically brought it back in Sonic Adventure 2 (under the name "Radical Highway") and chose it as the representative stage of this game in Sonic Generations.
Deader Than Disco: While initially praised by critics, the years after have not been kind to this game — in fact, the recent Xbox Live and PSN port has been savaged by critics. However, fans and gamers, as well as indy reviewers like The Video Game Critic have been much kinder to the game, and the Xbox Live version is now one of the highest rated games there. A number of the professional critics also made it clear that they considered the game itself So Okay, It's Average or even decent, but took it to task for the sloppy porting job (tellingly, the subsequent Sonic Adventure 2 port, which was a full HD remaster, got much better reviews).
Esoteric Happy Ending: At the end of Super Sonic's story in SA1, Tails says "all's well that ends well," even though all of Station Square had just been demolished and flooded by Perfect Chaos's rampage, and at least half of the population had to have been killed.
And in some way, Eggman becomes a Karma Houdini after having done the wrong to the city and its population and getting away scot-free, although getting the Egg Carrier II destroyed by Perfect Chaos arguably counts as karma.
Franchise Original Sin: This game was the start of many habits of future Sonic games, including the cliche of Sonic using the Chaos Emeralds as an Eleventh Hour power-up, as well as the cliche of Eggman being upstaged by a Monster of the Week that goes out of his control.
Not to mention some glitches in the game that allow characters to enter usually inaccessable areas or play around with unused content in the game (there is a glitch method for nearly every character to get into Emerald Coast for example). Granted a lot of them have the potential of screwing up gameplay or save data.
Possibly not a bug, but if you use the Light Speed Attack when fighting Chaos 6 as Sonic, it'll do double the damage and you can beat the boss in under a minute.
It also works if you have the Fighting Gloves and use the Maximum Heat Knuckles Attack when playing as Knuckles.
Harsher in Hindsight: In the Last Story, Perfect Chaos floods Station Square, leaving the city a destroyed mess, and no doubt drowning many people. Fast forward to 2005, and we have Hurricane Katrina completely flooding New Orleans and killing over 1800 people. Flash further forward, and you have the tsunami and earthquakes in Sendai, Japan. Then, a year after that, Hurricane Sandy in 2012 caused another disaster.
The intro depicts Perfect Chaos crashing through a skyscraper, and then 9/11 happened almost exactly two years after the game's release,
Also the fact that after you finish E-102 Gamma's storyline, he dies shortly afterward. This becomes worse when you realize that his English voice actor died shortly after this game was finished, and Sonic Adventure 2 had just been released.
Moral Event Horizon: The Echidnas trampling and killing the poor chao standing in their way just to get to the Chaos Emeralds and the Master Emerald. They didn't have qualms about taking down Tikal either (she wasn't killed though); even her FATHER Pachacamac didn't care, just as long as they seized the emeralds. This wasn't a very good idea.
If you exploit a glitch that allows Knuckles to reach Sky Deck through the Egg Carrier's swimming pool, you'll enter his flackback with Tikal as normal, but there will be no dialog whatsoever. Even when you reach the area where the emerald shrine is on fire and Tikal and the chao are laying on the ground, no cutscene plays, making it seem as though they're all dead. The kicker? You're stuck here forever. If you quit the game and return to Knuckles' adventure, he'll still be there with nothing to do but watch the shrine burn endlessly. The only way to fix it is to start a completely new file.
The Scrappy: Big the Cat for a great many people, and not just because of his levels.
Base Breaker: Of course he has garnered a plausible fanbase over the years to balance it, especially following his cameos in the latter title below.
Scrappy Mechanic: While all of the 3D games have bits of this, SA1 has one of the most loathed in the form of Big the Cat's fishing stages. If you jiggle the control stick even slightly the wrong way, you don't get the fish on the hook, you move the line the wrong way, and you have to reel it in exactly right or it will just magically get off the hook, at minimum stress, when it's right next to you.
Hunting for Emerald shards is also well-hated.
Seinfeld Is Unfunny: Despite being one of the first 128 bit video games ever released, one of the flagship games of the Sega Dreamcast and a critical darling when it first came out, many note that this game does not stack up well to its much better-designed successors in hindsight, which probably contributes to its Deader Than Disco status mentioned above.
As noted above in Franchise Original Sin, this game also introduced a lot of things that would become cliches in the series like Robotnik getting upstaged or the Chaos Emeralds being used as an eleventh hour power-up. At the time this was all fairly revolutionary for the games (Robotnik had never been eclipsed as a threat by another villain) at the time, but they got overused so much that it seems trite.
That One Side Quest: Try the Ski Slope Snowboarding mission in the DX version's mission mode and you'll find it very hard to not go crazy trying to beat it, to add insult to injury you can't save the mission as your last one or you risk running into a game breaking bug that courrupts your save file.
That One Level: Hot Shelter as Amy. It's not especially difficult, but it's like the level equivalent of Goddamned Bats: very long and full of annoying mechanics like doors you have to open by twizzling the analogue stick (which, if you have the PC version of SADX, means mashing the arrow keys in the correct order) and key hunts. Meanwhile the robot Zero is chasing you and putting you under constant pressure the whole time. No wonder the developers gave it an A-Rank time of 6 minutes 30 seconds...
Most of this is because Sonic generally visits the majority of any given stage, but Sonic never goes to Hot Shelter, so Amy gets the job of showing the level off instead. Amy's playstyle deals with slower gameplay than Sonic's does.
Some of Sonic's A-Rank levels are horrendous, and the first level (Emerald Coast) is a prime example. It's a fairly straightforward level to run through on the C and B levels (finish the level and finish with 50 rings, respectively). For the A-Rank, though, you have only two minutes, forcing one to spindash almost nonstop through the entire level while taking all of the stage's normal shortcuts (as in the ones the developers wanted you to take, not Game Breaker shortcuts found by speedrunners). It gets worse with levels like Red Mountain and Lost World, to name a few.
They Wasted a Perfectly Good Plot: The game goes into detail behind the history of Chaos, the Chaos Emeralds, and the Echidna tribe. One would think Sonic Team would use the stories to also expand Knuckles' backstory as well, but Knuckles actually has less interaction with the past compared to the other playable characters; Sonic and Tails get the most information regarding events from the past.