Individual players either come to praise the game's daring approach or despise it as an exercise in frustration due to the brutal difficulty.
A number of players also dislike the art style and certain songs, while the rest find them good.
The ending's take on the events that bridge the Classic and X timelines. Some think it's really awesome and love the connection, others don't mind it, some feel it could be handled better and there are those who consider it an untouchable plot point and felt offended by the game's pretentiousness. Others still feel that having the game end with an unwinnable boss fight ends the game on a sour note.
Fridge Brilliance: In Rainbow Man's stage, aside from the prism enemy, the only other enemy is a leprechaun in a pot that tosses out gold coins. Why's that? Well what do you find at the end of a rainbow?
Game-Breaker: Prototype Zero. You have to have already beaten the game already on original or instant death, so it can't be used to cheese the game as soon as you start. He starts out weak, and grows more powerful the more bosses you beat, but even if you only beat a third of them, he completely punches a hole through a good portion of the game's difficulty.
The top of Trinitro Man's head is intended as Schmuck Bait as hitting it causes a lot of damage but hitting it three times causes it to explode. If, however, the 3rd hit's damage is enough to KO Trinitro Man, the head does not explode and you win.
Using Glue Man's weapon, you can zip through walls similar to the bugs in earlier classic Megaman games. It was patched out in a later version, but demand caused the devs to release a "Speedrunning version" that reinstated the glitch, along with adding a few features, like an in-game timer.
Earlier editions of the game had a bug where Jet Man would randomly freeze in place, allowing players to simply buster him to death. Unfortunately, depending on when the bug happened, it could become a Game-Breaking Bug; this happened during Roahm Mythril's blind run, where Jet Man froze in place during his entry sequence, essentially freezing the game, and forcing Roahm to start the level over and play through it again.
In Zero mode, you play as a rogue prototype robot who constantly lose health, and the way to stay alive is to kill enemies. In Mighty No. 9, Ray's gimmick is exactly that. It also helps that she's an Expy of said character.
Prototype Zero being able to shrug off everything or simply parry everything that Mega Man throws at him becomes this after you see the episode featuring Zero in Death Battle. He's estimated to be tough enough to survive the explosive force of an impact similar to the meteor that killed the dinosaurs.
"Holy Shit!" Quotient: Highlights include Proto Man getting infected and turning on you, Bass going rogue, and the fight with Prototype Zero in the finale. The ending bridges the Classic and X series.
Hype Backlash: After coming out of years of development, the game's extreme difficulty level and other issues weren't received too well by a number of people.
Memetic Mutation: "So, like a normal Mega Man Unlimited level." Explanation It's become a meme from both detractors and people who like the game to say this in response to Marathon Levels in other games, either by describing the level in detail or using it in response to someone talking about a Marathon Level in another game, the joke being that all the levels in Mega Man Unlimited are Marathon Levels in and of themselves.
Yoku Man has an attack where he will make death spikes appear one tile above the ground in a row, except where he is about to appear and right beside him. If you didn't make it through his previous attack pattern properly, you're almost certain to die, unless you get lucky.
Jet Man's bombs. If you're on the right side of the screen, you get about a second to dodge or counter the bombs (and they don't fall straight, unlike the bombs dropped by the regular enemies). If you're on the wrong side, then you're just screwed. This attack gets an upgrade with his Omega form where he carpet-bombs the whole arena, giving you less room to dodge before they explode. Jet Man's other attacks can be dodged consistently, but this attack alone makes him a borderline That One Boss.
The Captured Wily Stage 1 boss's electrifying ladder attack. One hit while on the ladder it affects is enough to send you into a bottomless pit. Its other attack is annoying as well, since one hit from it will also ensure your death.
Glue Man has a fast pace. He also deals a lot of Collision Damage. His Omega form is even worse, as he now shoots three glue shots at a time as opposed to one, and his collision damage has been increased.
Jet Man can also pose quite a challenge. Not only is he quite fast, but his attacks all cause small explosions, come quickly, and do lots of damage. He also doesn't give you many opportunities to hit him.
Yoku Man summons yoku blocks, then teleports to a random yoku block and fires a fast moving projectile at you. After three yoku blocks, he teleports to the bottom of the stage and fills it with spikes, except for a small area in front of him. On the bright side, if you got Yoku Attack prior to the fortress, you can serve him a taste of his own medicine in the Boss Rush. He's absurdly weak to his own weapon.
The crab boss at the end of the first fortress level is also aggravating. You fight it on a set of three ladders over a Bottomless Pit, where getting hit by anything is almost guaranteed to be fatal thanks to the Knock Back. Coming in with a stock of Beat Whistles is highly recommended.
The fight with Bass, and then the two-form Wily Machine. None of the fights are particularly hard, per se, but they come one after another with no chance to regain lost health or weapon energy without an E- or W-Tank.
Rainbow Man's level, which is loaded with Quick Man death beams. It even gets worse, as some of the beams will pass through prisms that fan the light out into a wide area. It got toned down as of version 1.1.0, cutting out a number of potential cheap deaths, though the stage is still quite challenging.
Captured Wily Castle Stage 4 is a prime contender, even accounting for the fact that it's a Fortress stage. 9 Robot rematches complete with gimmick mini-levels prior to each rematch and a 3-part final boss battle all in one stage. It is enough to make players rage. Doubly frustrating if you haven't been through Yoku Man's level.
Captured Wily Castle Stage 3 is long and filled with Gravity Screw, and if you haven't been through Yoku Man's stage, you're introduced to the concept of Yoku Spikes of Doom here.
Jet Man's stage, which involves a long portion over a bottomless pit, which you must cross using platforms that move when you run the opposite direction. This is while steady streams of enemies jump up from the bottomless pit, and a pair of enemies perform what can only be described as an air raid. If you get hit by any of these, especially in midair, instant death is pretty much guaranteed.
Tough Act to Follow: Since the game came out years after the release of the well-received Mega Man 9 (which Unlimited was initially intended as a follow-up to), this was bound to happen. It doesn't help that Mega Man 10, which came out during its development, looks like a more well-balanced game in comparison.