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.
Adaptation Displacement: You probably won't find a lot of people who have even heard of Shrek! by William Steig (and if they did, it's likely they first heard of it by watching the credits of a Shrek film). So much was added to this little story that about the only thing it and the movies have in common is...a grumpy ogre named Shrek, a donkey (who is quickly forgotten about), a brief obstacle of a dragon, and an ugly princess.
Subverted with AU!Puss In Boots. He starts as lazy, fat housecat, but regains his badassery when the time is right.
Played straight with Shrek himself in Shrek the Third, which was noted by several reviewers. In the first movie, he curbstomped Farquaad's knights. In the third movie, he's much softer, and didn't do much to fight back against Charming. Shrek gets some of his badassery back in Forever After, but is largely overshadowed by the Proud Warrior Race Guy ogre tribe.
Though it did give us our first look at Fiona's badassery.
The Welcome to Duloc song can be seen as one too.
The "Do You Know the Muffin Man?" exchange.
Well, it does become a Chekov's Gun of sorts in the second movie.
Contested Sequel: Shrek Forever After. To some, it's a mild improvement on Shrek The Third but still not a very good movie. To others, it's a huge improvement with an interesting plot, tons of Continuity Porn and a great villain, and indicative of DreamWorks Animation's beard-growing. While to others, it's worse than Shrek The Third, completley abandoning the actual characters and a waste of time.
Both covers of "I'm a Believer" (Eddie Murphy's in the movie, Smash Mouth's on the soundtrack) are awesome, but Donkey belting it out at the end of the first movie with a crowd of fairy tales backing him up deserves special mention. For a typical kid watching this movie back in the summer of 2001, that whole sequence was the epitome of cool.
Filler/Padding: The entirety of Shrek the Third could arguably be considered this in relation to the series as a whole. The film has no major plot events that affect Shrek Forever After (aside from witnessing the birth of Shrek and Fiona's children, and the death of King Harold and Prince Charming) and none of the newly introduced major characters even appear in the subsequent film. Seriously, try watching Shrek, Shrek 2, and Forever After in that order while skipping over The Third. It has almost no bearing on the other 3 films.
One of the jokes MAD made about the first movie was Donkey and Dragon having half-donkey, half-dragon babies...which is exactly what happened in the second movie.
Prince Charming is the spitting image of Jaime Lannister from Game of Thrones. Not to mention the first movie dealt with a short maniacal nobleman in a red suit...
In the Japanese dub of the films, Koichi Yamadera voiced Donkey. The hilarity came with the fact in the very first film, the villain Lord Farqadd was voiced by Masato Ibu, who voiced the original Dessler and Shrek and Donkey has to defeat him. A few years later, Yamadera himself ends voicing Dessler as well.
Take another look at Prince Farquaad's royal seal in the first movie. It looks almost identical to the Facebook logo.
One of Shrek 2's jokes in the intro montage has Shrek getting caught in a trap where he hangs upside down and gets mud on his face, which Fiona wipes off and kisses him while he hangs upside down, in a parody of Spider-Man. Due to the fact that Disney owns Marvel, which Shrek is notorious for swinging at, this becomes very amusing.
Jerkass Woobie: Prince Charming. After enduring grief and humiliation now that he no longer has the power his mama gave him, all he wanted was his own Happily Ever After...which he probably would have gotten had he not stayed a villain by choice.
Love to Hate: Rumpelstiltskin in the fourth movie, for being more downright nasty and vicious than the previous villains while remaining Laughably Evil.
The tagline of Shrek 4 was "THE WAIT IS OGRE!" As a result, mentioning Shrek on /co/ will often result in a Hurricane of Ogre Puns. The most notable example is this fanart getting captioned with "I'm sorry Shadow... but my time here is ogre."
"Check yourself before you Shrek yourself."
"I like that boulder. That is a nice boulder."
"Brogres", people who parody the Periphery Demographic phenomenon by treating every Shrek-related work as masterpieces of the highest quality, getting together on Shrekchan, their Imageboard, where they tell stories where they encounter Shrek and other characters from the films in Real Life (usually to brutally maim non-believers and engage in "shrexual" encounters), and treat Shrek as a god.
Seen in the flashback in the alternate-universe when Rumpelstiltskin is shown completing the deal with Fiona's parents to make "their problems go away", doing so by making them go away. That would have also happened if the messenger had arrived a few seconds later at the beginning of the movie, but we don't know that at the time. When we see the king and queen's looks of indescribable horror as they realize they're being erased from existence, Rumpelstiltskin crosses the line from just a simple trickster who wanted to rule the kingdom into utterly, irredeemably evil.
The Fairy Godmother could be seen as a JerkassKnight Templar at first...up until she decides to use a potion to make Fiona fall in love with Prince Charming.
One-Scene Wonder: Robin Hood and his merry men get a lot of attention from fans despite their very brief screen time.
Periphery Demographic: But of course. All four films were written with family audiences in mind, meaning lots of slapstick humor for the kids and pop-culture references and Getting Crap Past the Radar for adults. And then you have the Brogres, who pretend to absolutely worship the franchise and treat it as a form of higher art (and even a religion).
Rewatch Bonus: The scene in the second film where Puss prays for mercy by explaining that he's trying to support his family becomes way funnier if you've seen his spin-off movie: he's making the whole thing up.
And after Dreamworks themselves grew the beard, other studios followed suit - instead of making Shrek ripoffs, they themselves started more frequently producing originaland well-likedCGI movies.
Sequelitis: This is the general consensus for Third. Fans are divided between whether Forever After is just as bad as Third or better. Reception has been much warmer for Forever After than for Third, however.
Ship Tease: Uhm...This. Especially the way he says her name at the end.
Spoiled by the Merchandise: Plush toys of Shrek and Fiona's triplets were in stores and on shelves at various different retailers long before the release of Shrek the Third, in which Fiona breaks the news to Shrek that she's pregnant.
Squick: at the end of Shrek 2, Dragon shows up with several of her and Donkey's newborn children. You don't want to think too hard about how that happened.
The alternate universe Donkey lampshades this when he asks Shrek about his children.
Donkey: "Are my babies cute, or do they make people feel uncomfortable?"
They Wasted a Perfectly Good Plot: A charge thrown by some at the fourth film, which presents a Bad Future wherein Shrek was never born and never met his true love Fiona. It would have been interesting if someone else was Fiona's true love and seeing Shrek deal with that, but Fiona loves Shrek regardless.
The fact we never see Dragon's beautiful form. Word of God is that they considered turning her into a Pegasus.
Tough Act to Follow: Zigzagged with Shrek Forever After. As it came on the heels of the poorly-received Shrek the Third, it wasn't hard for it to improve on its predecessor. However, it also only came a few months after How to Train Your Dragon, DreamWorks' best-reviewed movie to date, and also had the first two Shrek movies to live up to.
Unintentional Period Piece: The movie's soundtrack features Smash Mouth and the Baha Men, and it stars Mike Myers and Eddie Murphy, two men whose careers have cooled off considerably since the movie came out.
What Do You Mean, It's for Kids?: The fourth film gets pretty dark sometimes, people. From the malicious Rumpelstiltskin who erased Fiona's parents from existence and murders people (even his own followers) for his own amusement, to the Crapsack World that AU!Far Far Away becomes, there are some dark themes explored in this film.
Also a heavily Bowdlerized version of Matt White's "Best Days" appears in the credits of Shrek the Third. Parents who bought the song may be shocked when he says "lying naked under the covers"
Woolseyism: The Polish version is arguably funnier than the original, at least to Poles.
Same applies to the Hungarian version (and every other localization, I'm inclined to believe), with an extremely clever choice of voice actors and well-adapted cultural references.
Banderas does the Spanish version too - with an Andalusian accent.
That, however, doesn't prevent the Latin American localization from largely being a subversion, as it sports heavy Mexican accents, idioms, and at times jokes a little too localized, which made the movies right down unbearable for many of the non-Mexicans (arguably most of the targeted audience)...
The same problem occurred with the French version; while very well-localized for the French, it was considered incomprehensible by people in Quebec and some parts of France (to the point that one Québécois politician attempted to pass a bill requiring Quebec French dubbing for all movies after seeing Shrek the Third in French).
The Hebrew version is god-awful. But, then again, the only thing that's better in Hebrew is Crime and Punishment, and that's because they replaced Crime with Sin.
The Dutch version was also pretty good with the Woolseyism. Whether the original is better than the translation is subjective, though.
The Austrian version had a different voice Actor for the Fairy Godmother than the German version.
Shrek Video Games:
Hilarious in Hindsight: After Shrek Forever After has been released, it is rather hilarious to frequently fight witches in an adaptation of the preceding film.
In the first game, Humpty Dumpty and a giant mother goose appear in the same level. Puss in Boots features the two as major characters. Humpty is even a villain, just like in the game.
It's Easy, so It Sucks: Frequently the case with these games. A shame, because in Shrek The Third at least, there actually was a decent amount of effort put into the enemy design and variety, but it goes to naught because of overly powerful Regenerating Health and enemies not dealing sufficient amount of damage.
No Problem with Licensed Games: Shrek SuperSlam, a fighting game, has a decent Metascore of 67. This is also parodied by the Brogres treating Shrek video games as must-play masterpieces of the highest caliber, just like with the movies.
The pinball machine has also been received pretty well, being ranked 93rd overall on the Internet Pinball Database with a 7.8 average rating out of 10 and earns a good amount of money in public. It may have been a Palette Swap of Family Guy, but it had better sales too.