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.
Author's Saving Throw: Sega released a patch for the Wii U version that addressed concerns from fans. Collecting 100 rings grants you an extra life once more and Sonic now starts with double the amount of lives that he did previously. Furthermore, the Wisps that had to be controlled with the gyroscope can now be controlled with the analog stick and buttons.
Best Boss Ever: The final battle with Eggman is easily the most exciting boss fight in the game, easily resembling the final fight from Colors, and is accompanied by awesome music. Especially considering it follows the lackluster boss fights against the Deadly Six. The only downside is that the final boss is still incredibly easy, but it's still the best boss this game has. It is, however, more difficult and involved in the 3DS version.
Desert Runs Zone 2, for capturing the appeal of Generations while also awesomely integrating the features of Lost World, complete with an awesome song and unique boss battle.
The Legend of Zelda Zone, due to all the Zelda Mythology Gags, the amount of detail put into it, the music, and Sonic wearing Link's outfit exclusively for the level.
Tropical Coast Act 1. Out of all the "normal" levels in the game, this one has the most diverse environment, with a ton of alternate routes and platforming to do. Plus, if you're really good at the controls, it's massively fun to just spin dash past everything.
Hidden World act 3. The only Hidden World act without a gimmick to it, it is instead a surprisingly challenging Bonus Level of Heaven. Nearly every single surface is temporary and nearly every single surface is also covered in rings and animal capsules. Easily one of the most rewarding and cathartic stages in the entire game, with a snazzy soundtrack to go with it.
Broken Base: Because some things never change. As per the usual reactions to modern Sonic games, various things about this game have been debated; from the Nintendo exclusivity, to the change in art style and gameplay, to the plot and characters, and almost anything else you can think of.
Character Rerailment: Amy, surprisingly enough. In a leaked cutscene, Amy is seen comforting the animal friends that Sonic has recently freed. In games like Sonic Adventures 1 and 2, Amy can be shown being a caring person in cases like the Flicky from Adventure 1, and this aspect of her character was nearly forgotten due to the character's Flanderization. Not once has Amy gushed about Sonic in the entire cutscene, and she was even seen having a normal conversation with him through the MilesElectric. Over the course of the entire game, Amy never even mentions her crush aside from the scene where she appears to die during the Deadly Six's world-draining.
Tails, likewise, gains a bit of independence towards the end of the game that he hasn't had since the days of Sonic Adventure.
Although it already happened in the previous two games, fans are pleased that SEGA is continuing to treat Eggman like a credible villain even after he gets betrayed by the Deadly Six. He even wins back his status as Big Bad at the end of the game!
Critical Dissonance: IGN gave it a "mediocre" rating of 5.8 while the community review is "amazing" rating of 9.0; though other sites have given it negative reviews, fans take this as either Follow the Leader or bias towards Sonic or Nintendo.
8.8: One can expect the response that occurred when IGN gave the Wii U version a 5.8, and then GameSpot gave it a 5.
Fashion-Victim Villain: In-universe; Zeena largely cares more about doing her nails and makeup than helping the Deadly Six take Sonic down.
Game Breaker: The ability to lock on to certain enemies multiple times before delivering a more powerful Homing Attack makes a joke of most of the bosses in this game.
The Yoshi's Island DLC. Each Yoshi saved gives you three extra lives. Combine that with the abundance of coins, and you can easily get over thirty lives in one run of the stage.
The patch that was released re-instated the ability to gain lives for every 100 rings. This ends up destroying the game, as ring collection is more to the tune of Sonic Unleashed, with you typically gathering rings in large clusters with totals reaching the THOUSANDS in some zones. Nightmare Zone, Desert Ruins 2, Silent Forest 1, Sky Road 1 and Hidden World 2 stand out as the most beneficial, and one of those can be accessed as early as when you get to the world map!
The extended Spin Dash, which is faster than simply running and can destroy enemies on contact. Unlike the Sonic Boost in Sonic Unleashed, Sonic Colors, and Sonic Generations, the extended Spin Dash never runs out of power. This was used to absolutely annihilate most of the S-Rank times in Time Attack and makes some stages much easier than intended, like Frozen Factory Zone 3 and parts of Lava Mountain Zone 3. In addition, enemies were definitely designed with Sonic's normal running speed in mind, such as the timing of the Ball Hogs in Silent Forest Zone 2.
Goddamned Boss: Zeena's first fight in the Wii U version is not too terribly difficult (none of the bosses are actually), but it makes up for it by being a Puzzle Boss. Zeena hides in snowmen during the fight and Sonic must destroy them all to draw her out. If he takes too long or hits a snowman with a bomb on it, the snowmen will reset and he'll have to start over. Compounding the difficulty is that he has to do this while trapped in a snowball himself, restricting his movements to running, jumping, and the Spin Dash. It's frustrating as hell for first timers.
Additionally, while most Sonic games featured space as the setting for their climax, not only the Galaxy-inspired Lost World lacks space levels at all; it also follows the very same grasslands-desert-beach-forest-sky-volcano order commonly associated with Mario games instead.
It's Hard, so It Sucks: A somewhat common complaint among those who dislike the game. It's a step up in difficulty from previous Sonic games, and when combined with the fact that the game is very stingy with extra lives, this game has proven to be very frustrating for some players. Better start grinding for lives in Windy Hill Zone 1!
The game's strange momentum makes it especially difficult for the wrong reasons.
Zazz's "I've been dreaming about pounding his sorry blue butt" line from a gameplay video has people snickering that the game sounds like a porn.
Sexy◊ Tails is becoming increasingly popular, to the point of almost reaching Memetic Sex God level.
Moral Event Horizon: The Deadly Six cross it when they activate Eggman's Extractor to drain the world completely of its energy, destroying it outright. They cross it a second time when they kidnap Tails to turn him into a robot, albeit by accident.
Rule 34: Hoo boy! Zeena might not have any feminine "attributes", but that hasn't stopped the fanart from pouring into the internet.
Scapegoat Creator: Some fans have taken to blaming Nintendo for the game's shortcomings all because the game was made under an exclusivity contract. Nintendo only put the game under contract, not got directly involved.
All of the Deadly Six. Not only are their character designs are out-of-place even for the Sonic series, their characterizations are so cliche yet minimal and the explanations for their existence are nonexistent, that it's hard to see the point behind them. See, They Wasted a Perfectly Good Character below.
Tails has gotten a lot of flak for his attitude in this game, namely how he berates Sonic for betraying his trust because he requests Eggman's help in stopping the Zeti and saving the world. This is despite the fact that Tails shows no objection to the team up prior and how he completely disregards Sonic's attempts to make up for his earlier Nice Job Breaking It, Hero that kicked off the problem in the first place. In the end it's Sonic that ends up apologizing to Tails, over something he never had any control over.
Holding down the run button forces you to run up walls that you don't want to. This isn't so bad in 3D sections, but in 2D sections, it gets aggravating when the game forces you to go at walking speed just because you don't want to run up a wall. This applies to almost any wall, even ones the same height as Sonic that you would have no reason to want to run up.
Many of the Wisps are controlled by motion, instead of the more intuitive, simple scheme used in Sonic Colors. Complaints got so great that eventually Sega fixed this by allowing you to control with the analog stick and buttons just like in Colors.
Holding down the run button on ice makes Sonic skate similar to Super Mario Galaxy. Unfortunately, jumping while skating gives you a fixed momentum that you can't change, making you jump into obstacles or enemies a lot of the time. Like the automatic parkour with the run button, being forced to go at a snail's pace just to have better control can be aggravating.
Auto-scrolling levels. In most other platformers, they're tolerable, but in a Sonic game of all things, they're just out of place and painfully slow.
That One Level: Lava Mountain. It's nearly Eggmanland levels of difficult, and even has a similar appearance. Especially Zone Two, which requires you to be precise with the jumping.
The second stage of Frozen Factory. It's a long stage where you control a large snowball with annoying controls through a maze full of holes and enemies that bounce you all over the place, before finally confronting the significantly less annoying boss.
It gets even worse if you're trying to collect all the red rings. While most of them are rather easy, the ring in the second pool table is incredibly difficult to obtain - due to the way Sonic bounces in the snowball, you have to gently nudge him in the right direction, which can be hell. To make matters worse, there's a checkpoint right after this section, meaning if you fail it you have to try and jump off of the table and kill yourself. If you fail this, then you're propelled right into the checkpoint and have to restart the entire stage.
Silent Forest Zone 3. The final Red Ring requires the parkour skill and jumping. Prepare to die and curse the game designer's descendants. A lot.
The Woobie: Sonic. He was already feeling pretty bad about endangering the world because of his recklessness, but things just get worse from there. His best friend gets captured and is planned to be roboticized, his other friends presumably get the life sucked out of them, and the last thing he sees of his only remaining allies is them falling towards a river of lava. No wonder Sonic is so distraught throughout the second half of the game.
Tails counts too. He gets injured AND captured due to Sonic's recklessness, gets converted to a robot (well, faking it anyway), and feels hurt because his best friend seems to trust the egomaniacal madman who tried to kill them for years over him.
The plot in general is considered a large step up from the last twogames, by actually developing the conflict this time, but is generally still considered pretty poor. This is due in no part to the execution of certain plot points, the lack of context to some story elements, and what is generally conidered a very lackluster third act. The consensus seems to be that it starts off well enough before dropping in quality halfway through.
They Wasted a Perfectly Good Character: Amy spends the story taking care of animals on Sonic's World, so she's not wasted. Knuckles isn't even there long enough to count as comic relief: He gets all of TWO LINES in the entire game.
Likewise the Zeti. They could've made very interesting and memorable villains, and while their character interaction is great, despite their cliche personalities, everything else is wasted. We know next to nothing about them, why they became the Deadly Six, where they came from, why they were sealed away, why the conch controls them, or what a Zeti even is! Not to mention their fate was VERY anticlimactic and ambiguous. Most we get is some vague little snippets of their relationship to each other and that's about it. Here's hoping Sega rectifies this if they plan to bring them back for future installments.