Author's Saving Throw: 3.6 adds in an alternate stage option, with the alternate stages being the original versions of the redesigned stages. This seems to be aimed to alleviate the complaints toward the Project M team's tendency to greatly alter or simplify numerous stages, which makes the stages feel derivative and boring.
Falco, whose animations were changed back to Fox's. While people who liked Falco above Fox in Melee are glad, people who have a distaste for true clones are not.
Lucario, whose signature Aura mechanic was removed due to allegedly "rewarding bad play". People who were drawn to Lucario by the mechanic in the official Super Smash Bros. games consider PM!Lucario to be a direct insult.
Ganondorf, carrying over from the official Smash games. There are many fans of the "Falcondorf" set from Melee who appreciate PMDT's attempt to compromise decloning with keeping the best of the Melee moveset, which entails keeping him a shadow-fisted brawler, but many others are calling for a complete moveset revamp that is in line with his home series, citing several moveset changes that make characters more faithful to their origins (including Wario with his Shoulder Dash, Samus using the Morph Ball to crawl instead of as a roll dodge, Sonic incoporating several moves from Sonic Battle as well as giving him a new side-special). And then there are others who want him to be completely "Falcondorf" and lament the changes to 3.5 (particularly the replacement of the Warlock Punch).
Some dedicated tournament players consider it better than any of the Smash games officially released by Nintendo due to its higher level of balance towards high-level play (when it's usually balanced at low-to-mid-level play), greater mechanical depth and greater speed and precision required to play.
As the game grew more complete, it began to be more universally accepted as its own installment in canon rather than just a modification of Brawl.
Broken Base: Plenty of members of the Smash community still prefer Melee or Brawl over Project M, though the situation has been getting better with big name Melee and Brawl players' participation.
Want to easily start a debate? Bring up whether Fox and Falco should be nerfed from how they were in Melee.note Basically, they're controversial because they're generally considered two of the best characters, but are also very fragile and have fairly tough execution.[[/note] In the final update, they were nerfed (Fox much more so than Falco).
One user had leaked Project M's Clone Engine and codes.[[note]]At the time, Brawl Ex hadn't been released, which is why it was leaked. It, among other things, sparked friction between KC-MM and Project M members, pushing onto light an Open Vs. Closed Source debate relative to Brawl modding.note Basically, some people felt that the Project M team, which includes some of the best members and technical advances of the modding scene, has a tendency to hog the best tools to be used only for Project M. The argument against that notion is said tools are functional but not perfect enough for the team to be comfortable with distributing publicly.
L-cancelling, pressing the shield button during an aerial attack to speed up the landing animation, is a hot topic of debate. Supporters say that it adds more options and makes the game require more skill to play. Detractors say that there is absolutely never any reason to not L-cancel that can't also be achieved by just waiting a few frames before the next input, so it should instead be done automatically rather than require what they perceive to be an unnecessary button press after every aerial attack. No other fighting game series controls in such a way.
3.6 finally included an auto-L-cancelling mode. Predictably, the community has been divided between "this has to be forced on in tournaments" to "it's alright for casual play and not for tournaments" to "this thing shouldn't have been suggested in the first place".
More recently, as Nintendo finally became more involved with the competitive Smash community, Project M has been excluded from several big Smash community events for being a Game Mod (a concept which, unlike some American PC game companies, Nintendo is likely uncomfortable with) as a legal precaution. Instead, the big promotion goes to the official Wii U / 3DS, which is still a good game, but does away with much of the "depth" that makes Project M (and Melee) so popular. This has left some people questioning whether having Nintendo's sponsorship (i. e. control) is worth the cost, and some people claiming Project M doesn't deserve to shine because it's an unofficial mod (rather than because of how well it plays as a competitive game).
Demonic Spiders: Fox, when controlled by the AI. While most characters' AI in Project M are relatively standard, if a bit more aggressive than standard Brawl, his AI is set to perfectly perform competitive-level techniques, hopping up and down repeatedly while spamming his blaster, spamming wavedashes and Reflectors, and being generally much more aggressive than the rest of the fighters. Even on low AI difficulties, Fox does these maneuvers. Most characters wait until higher levels to start pulling them off repeatedly. God help you if you end up facing Team Fox in Classic Mode.
There is a tense three-way rivalry between Melee, PM, and Wii U / 3DS. Melee supporters argue that the original is the gold standard that cannot be topped with PM being only a pale imitation, PM supporters argue that their game has overall improved on Melee, and Wii U / 3DS supporters argue that their game has been dismissed as "casual" far too early.
Game-Breaker: In just about every version before 3.5, there was always at least one (though the first demo's meta never developed quite enough to reveal any). The most infamous include 2.0's Ike and Lucario, 2.5 Sonic (which was actually a nerfed version of 2.1 Sonic), 2.6 Ivysaur, and 3.0 Mewtwo.
This game turns Jungle Japes into Skyloft, where players brawl on a floating stage that tours around Skyloft. Cue the reveal trailer for Super Smash Bros. for Wii U/3DS, and Skyloft is one of the stages to be revealed in the new game, with the exact same concept of a floating stage that also tours around Skyloft.
All of the stages in Super Smash Bros. for Wii U/3DS have a "Final Destination Mode", which turns them into something similar to the tournament-friendly versions of Brawl's stages featured here. Ultimate allows players to turn off hazards, making them resemble certain Project M versions of stages even further.
This game splits the Pokémon Trainer's trio of Squirte/Ivysaur/Charizard into three separate fighters. Super Smash Bros. for Wii U/3DS also splits Charizard off into a single fighter.
Speaking of Charizard, the Charizard in Wii U and 3DS has a claw attack for a forward aerial and its signature Seismic Toss as its up throw, just like the one in this game. The latter has been suspected of being a deliberate Shout-Out.
Zero Suit Samus, though already independently accessible in Brawl via an Easter Eggnote Hold the shield button during the character select screen., was made into a completely separate character with her own picture on the character select screen in Wii U and 3DS.
Dr. Mario and Mario were merged into one character in this mod, to the point of having Dr. Mario only be an alternate costume for Mario. In for Wii U/3DS, Dr. Mario returns as an alternative to the normal Mario meant to appeal to Melee players due to him being more popular than the normal Mario in competitive play.
Donkey Kong's dash attack in this mod is the Rolling Attack from Donkey Kong Country. SSB4 makes this exact same change. Similarly, Sonic in Project M has the Insta-Shield as a neutral aerial, a change which SSB4 similarly makes.
Even though the wait was long, Mewtwo and Roy were finally brought back proper in SSB4 as DLC. Roy's Flare Blade special also has him holding the sword more horizontally, as he does in Melee and this mod.
Lucario was turned into a Shotoclone with chainable moves in this game as a Shout-Out to Ryu from Street Fighter; it was even given an alternate costume (technically referencing the Black Belt class) somewhat resembling him. In June 2015, Ryu himself was confirmed as DLC for SSB4, with a very similar (but coincidental) gimmick.
One of the features brought back from Melee is directional air dodging. Super Smash Bros. Ultimate would itself bring back directional air dodging.
One of the common complaints from detractors is that the game increases the input window for a lot of Melee's advanced mechanics to make them easier for less skilled players. Other common complaints include criticisms about the ease of recoveries on most characters though this was addressed 3.5, and certain characters requiring a lower skill cap to match the output of high-skill characters (Fox and Falco, Melee's top/high tier stars, are usually the baseline for this).
It's also consequence of how the team approached making more characters viable. Some Melee players dislike that the overall design of the game is, compared to Melee, much more contrived (specifically in buffing many characters in non-standard ways to compete with Melee's high tier characters), which arguably made the game less about precise spacing and more about so-called moveset "gimmicks"note such as the abundance of effective projectiles and "auto-combos"note loosely defined as combos that are reliable within generous criteria, a concept not typically emphasized in Smash Bros.. On the other side, one could make the case that it's unfair to hate the newly-viable characters for basically just being different from the few high tier Melee charactersnote as opposed to the entire Melee and Brawl rosters, that some of the ''Melee''-viable characters also have non-universal mechanics and guaranteed combos, and that the 3.5 update of Project M actually toned down the over-the-top aspects of many of the characters. It's highly subjective.
The number "47" appeared in several videos and counting since the April Fool's Turbo Tuesday Samus video. It was the subject of much joking and speculation, but was later confirmed to be essentially meaningless.
"Woop woop," after the sound that Mewtwo's Up special makes. Crowds have even started chanting this in tournaments when Emukiller is ledge stalling.
Many characters who were considered useless in either or both the Melee & Brawl metas are much more viable picks against Melee standouts like Fox and Falco here. The gap between high tier and low tier is much, much smaller than it was in Melee, and Brawl especially. For example, Mewtwo went from being one of the worst characters throughout Melee's lifetime to being one of the best characters in this game (at least before 3.5), truly fitting its status as a Legendary Pokemon.
From a different perspective, Ganondorf. Various animation and moveset changes were done to him in response to complaints about him being a Captain Falcon Moveset Clone. Aside from that, he too has had his many problems from Melee, and of course especially from Brawl.
Saved by the Fans: Due to the leak of Project M's development build after its cancellation, some fans have already decided to try and create a completed version of the mod, featuring fully playable versions of the leaked characters as well as bugfixes.
Scrappy Mechanic: The fact that you can no longer pick up items while running like in Brawl to people who play with items on, anyway.
Though this tends to be the reaction with nerfs in any version, 3.5 was an especially controversial update at launch. Its purpose was to redesign many of the characters to generally play more consequently (e.g. have higher-commitment attacks, have toned-down recoveries note as to give edge-guarding opponents a greater advantage, et cetera). The fans were especially surprised that even some of the characters perceived to not be high tier in 3.02 were nerfed. Although 3.5 is well-accepted these days, players of certain characters still make the case that the dev team went too far with nerfs.
The changes to Lucario and Falco's movesets are considerably more heated among their Brawl and Wii U / 3DS players, and there is still a minority who prefer Wario's Bike to the Wario Land Shoulder Charge that he has now.
The new announcer from 3.6 has received this due to many fans saying he sounds flat and uninteresting compared to the old announcer. He was replaced with a new one, come the next update.
Win Back the Crowd: To the astonishment of everyone that didn't read the developers' past brief statements that something of the sort was a long-term goal, 3.6 seems to be trying to win back casual players via the Alternate Stage Loader engine, which allows one to choose the Brawl versions of the tournament-altered stages if they wish, or players who feel that They Changed It, Now It Sucks! about the remastered N64 stages to choose the original 64-bit versions. Given that PM as a whole is almost always accused of being a Fan Hater's project, this seems to be a bid to tell common players that they mean no ill will towards Brawl and its fanbase.