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.
Awesome Music: Duh. It's about time that the series' track record finally gets used as it deserves. Only this time, given the game's based on music, the developers aren't really allowed to screw up. Chris Kohler, of Wired and Power-Up full title: "Power-Up - How Japanese Video Games Gave The World An Extra Life" fame, put it best:
Game Breaker: Each of the original 13 base characters has a Limit Break type ability learned at Level 40. For Warrior of Light, Firion and Terra, it activates when you chain so many notes in BMS, and respectively reduces damage by half, restores HP for every successful note trigger, or triples the damage of offensive Magic. Lightning got an ability to boost Strength and Magic by 75 each, and the other nine got a super-attack that they use against bosses and do heavy damage based on their stats, and they will use it against every boss if you do well enough to meet more than one. If it sounds like these abilities are good, they are. With as little as two of the damaging abilities on the right characters at Level 99, the bosses that are supposed to be the toughest enemies in the stage will die on arrival, Warrior of Light and Firion make stages much easier, and Terra's offensive magic is brutal. The developers apparently took notice how good they are, because these abilities were removed from the iOS port. A number of characters still have them in the sequel, but exactly how badly they break the game in it is yet to be seen.
Good Bad Bugs: YMMV if it's good, but in Field Music (only), letting go of holds late still results in a Critical, as long the vertical position is good enough and you don't hold it so long as to get a miss.
Internet Backlash: The iOS port of the game gives you the base 13 characters and two songs, other characters and songs, some of which weren't available for the original game, cost money for download. When someone sat down and did the math to find out the total cost of all the extra content and found it works out to well over 100 dollars, the fans were not impressed.
In explanation, defeating Chaos and seeing the end credits requires only a few hours work. However, unlocking all the content in the game takes much, much longer: you keep getting new stuff every 500 Rhytmia until you reach 99999, and you can only get around 130+ per song if you do well. While you might be able to get all the shards to unlock every character much faster from Dark Notes and silly titles, songs for the sound test and movies for the movie player might not hold much value for you, you still need at least 45000 Rhytmia to unlock the last extra song in Challenge mode.
It's the Same, Now It Sucks: Some people don't like the fact that the tracks are not remixed except for only a few exceptions such as Mt. Gulg, with this particular example being taken from the various remakes of the first game instead of the original 8-bit version. Given that the game is meant to be a tanker truck of nostalgia fuel though, this is more than likely intentional. .
Porting Disaster: In addition to being laggy, the nominally "free" iOS version only includes 2 songs and 13 characters, and purchasing everything costs more than three times as much as the 3DS version — which already includes all of this premium content, except for some songs which are either still DLC or just not available as well as some characters that don't have any unique skills available to them.
The Stoic Bonus is a bit of an odd mechanic. Putting on equipment makes songs a little easier to survive and\or lets you earn more items (depending on what you equip), without affecting your score. Removing all equipment results in a huge score bonus (about 2 letter grade's worth). So the game creates a choice between playing with equipment so you can get more items, or playing without equipment so you can get a better high score. Playing stoic also removes the special features from the songs. Thankfully, it's been removed in the sequel and you can now get a maximum score on any song right off the bat regardless of equipment if you do well enough.
Surprise Difficulty: The game is full of sparkles, cute cartoon characters, brightly colored and rounded icons, and aside from maybeBarbariccia and some of the more frightening enemies like the Ahriman and Anima, there's nothing a Moral Guardian would object to. The higher difficulty songs will crush your spirit, trample the shards laughing, and invite you back to more. You will wish for the comparatively simple task of just fighting Omega and Shinryu like normal, rather than getting a perfect 200-Critical chain on Ultimate Difficulty with no abilities and starting over any time your timing is off just enough to miss that one Critical.
Tastes Like Diabetes: Chibi Vivi, especially when he hops and swings his little staff. Add the fact he might appear on the main menu and say his quotes from his game.
That One Level: If playing the songs in game order on Ultimate, Battle With The Four Fiends will make you cry; and that's not even nearly as hard as Battle at the Big Bridge.
And those are just among the songs that are part of the main game. Some of the DLC songs on Ultimate continue to reach a new level of evil each week!
That One Sidequest: The trophy for defeating Chaos in a Dark Note. First, he only appears in Dark Notes that are at least level 90 (out of 99). Second, he's always Boss No. 3. Third, he doesn't always appear in a Dark Note of that level, so a player may have to clear through dozens of level 90+ Dark Notes to find him. Fourth, presuming you do find him, he has a ton of hit points, which means you need a lot of power and abilities to clear through him. Fifth, the spinning arrows mentioned under Scrappy Mechanic are guaranteed to appear during the fight. And, finally, he does a ton of damage, so a couple of missed notes can mean having to start over. It's like combining a Metal Slime with a Final Boss, and mixing in a Scrappy Mechanic for a garnish. Good luck.