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.
And You Thought It Would Fail: Many people had doubts that this series would be a success. Instead the Skylanders series has crossed the $2 billion in sales threshold, with over 175 million toys sold since 2011, it makes the series one of the top 20 highest-selling video game franchises of all time!
Broken Base: There are some fans that are willing to at least give it a chance or actually like it, despite the negative outcry from a lot of them. Some are happy that Spyro's personality is supposed to be like his Classic Self.
Cynder broke the base again. Legend fans were quite pleased, Classic fans weren't. Many fans wanted a clean break from previous continuities...
There's a displeasure within both the "Classic" and "Reboot" Spyro fans that this series is less of a Spyro reboot and more of a series that includes Spyro in it. The fact that there doesn't seem to be a new Spyro game coming out anytime soon leaves fans worried that the series will befall the same faith as its rival, Crash Bandicoot.
Some Skylanders even break the base. Sprocket for example has some people hating her just because she looks "too human", while others think she's a refreshing change of pace in adding some diversity to the teams. Some merely dislike her because they already have her and they have to wade through dozens of Sprockets to find what Skylanders are available in the stores next.
Critical Dissonance: Fans were really not looking forward to it, and many are making a big deal about how little respect they have for the game or hope in its ability to sell. Critics, meanwhile, are often very warm to the new game, taking it for the toyetic kids' game that it is, and quite like it.
Demonic Spiders: Missile Mauler trolls in Swap Force. Unlike most ranged enemies, their regular attack fires a homing missile that redirects towards you once and deals a HUGE amount of damage (120-ish on Medium difficulty). They also tend to be positioned on elevated areas or on the far end of the arena, which means that they're going to fire that missile at least once.
Spyro has become this because he's, well, Spyro. He's no more important than the other characters but has a major following.
Flashwing is also pretty popular, probably due to being voiced by Tara Strong.
Fridge Brilliance / The Dev Team Thinks of Everything: Jet-Vac flies using the vacuum device on his back, which depending on your upgrade path is limited duration... however using his secondary attack (the vacuum mode on his gun) starts to refill it.
Fridge Horror: Like you, Kaos and his mother are portal masters... however, Kaos's mom actually uses her powers to Interface Screw, and speaks directly to the player - she knows how to fight a fellow portal master, and is Genre Savvy enough to attempt to attack the player. Just imagine if Kaos learned how to do this...
From Spyro's Adventure, we have Terrafin and Ghost Roaster who are really good at dodging, Hex who can set up a super-powerful wall while she safely fire away from behind it, and Boomer whose ground pound attack hurts a lot of targets at once and stuns.
From Spyro's Universe, Tech Skylanders are really good for the Sky Defense minigame, where their machine gun Limit Break can mow down multiple mooks with ease.
From Swap Force PvP, we have Bumble Blast. His bees can be fired at a good rate, home in on the enemy, and hit more than once. He also has honey and mines which make the opponent slowed for some time and also makes them take more damage from bees. Then there's Jolly Bumble Blast, who is Bumble Blast wearing a Christmas hat that boosts his speed and armor by a huge amount.
Dune Bug in Swap Force's Story Mode. An early upgrade allows his Dune Balls to trap up to 5 small/medium enemies (bypasses shields and hits flying Rip-rotors), then he can roll them off the edge for a One-Hit Kill. As Skylands is a World in the Sky, he has many opportunities to do so, and if there isn't he can fire the ball at a wall to stun the trapped enemies. As such, the only Mooks Dune Bug usually has to worry about are Geargolems. This ability is mostly useless in PvP, though.
Growing the Beard: Some people believe that in between Giants and Swap Force, the series started to take itself a little more seriously. Giants started adding a lot of well-known voice actors to the cast. (Just take a look at the Trivia page!) The toy designs became more detailed, and the games started gradually adding more to the gameplay, such as the ability to jump. Not to mention, the levels of Swap Force are not only better looking than in Giants, they are much more full of secret areas, some of which are relatively well hidden.
Additionally, Swap Force began featuring more nuanced combat styles among the Skylanders themselves. While still in simplistic, kid friendly forms, Stance Systems, Status Buffers, Beastmasters and more are present, rewarding players who take a more strategic approach to combat.
For some, making fun of that one Skylander who the stores always have a ton of that you already have.
Mood Whiplash: The Skylander's backstories can vary wildly in tone. On one hand, there are characters like Whirlwind (a full-on Tragic Backstory which deprives her of her children) and Wham Shell (the troubled prince of an undersea kingdom) with serious and dark backstories. On the other hand, there are completely silly ones like Shroom Boom (a mushroom who escaped being turned into Kaos' pizza).
Scrappy Mechanic: While the figures certainly cater towards the collector demograph and is the Dancing Bear, the Merchandise-Driven aspect has created a minor annoyance of a Scrappy Mechanic - the fact that certain Skylanders are more rare than others, and that not all of the Skylanders are released at once. This can lead to certain Skylanders who the stores never seem to run out of and other figures that the stores never seem to carry. Not to mention, certain Skylanders never got a series 2 or series 3 rerelease, meaning that as stores carry less Spyro's adventure packs, it becomes harder to find the non-commonplace Series 1 Skylanders, same with the battle packs.
Sunburn and Ghost Roaster deserve special mention, as their figures are only available in the Dragon's Peak and Darklight Crypt packs - which have been out of print for several years and, consequently, become much harder to find in a brick-and-mortar store. Furthermore, Darklight Crypt was fairly rare to begin with, leading to sightings of it in secondhand stores for almost $200.
As mentioned by Chris Bores, certain Skylanders tend to be purchased immediately by collectors, who then sell them on ebay or Amazon for inflated prices. This makes certain figures a little more rare.
For some time, Ninjini was so rare that stores which carried Skylanders reported a ratio of one Ninjini figure out of forty other Giants being shipped. Like Spy Rise and Stink Bomb mentioned below, it was not uncommon to find her online for four times her retail price.
Self-Fanservice: just check at Deviantart, you'd be surprised how much arts there are about naked Stealth Elf, often with very exaggerated curves when compared to the skinny action figure.
Hex got some of this too; werheas her actual dress is rather sober and cover everything but her face and fingers, you will probably easily find art of her in Stripperiffic goth attire with Absolute Cleavage, when she even wears something. And of course, don't expect her to have decayed skin or anything similar : they apparently forgot she was suppposed to be an undead.
It doesn't take long for Ninjini, Chill and Sprocket to get fan-serviced either. As a deviantART member once reacted:
"God dammit....you just cant stop yourselves, can you? Gotta draw EVERY HUMANOID Skylander like she's some kind of god damn porn star!"
Shipping: while the game doesn't provide any visible romance between the Skylanders themselves (due to their personalities and relationships never being explored except in the biographies and trailers), this hasn't stopped the fans from already imagining some shippings. Aside from the obvious Spyro/Cynder due to them being based on Legend of Spyro, Flameslinger/Stealth Elf seems to have become quite popular (logically due to the fact both are from the same species).
Even Les Yay have been imagined already, mainly with Stealth Elf/Hex.
That One Achievement: In Giants, only one of a character's "Quests" cannot be achieved in single player — it requires winning 10 PVP matches, and you can't Gold-rank the figurine without it. Do you have friends to challenge?
In SWAP Force, one of the Portal Master achievements requires you to own at least one Sidekick... because you got it, right? Surely the toy stores haven't decided to stop carrying all the sidekicks...
For collectors, there is that one figure that you can never find - it's always online for a much higher price than you're willing to pay for it.
Tear Jerker: The Machine Ghost's Disney Death in Giants.
Sonic Boom's backstory is painful to read.
That One Sidequest: Some of the Heroic Challenges can be a nightmare for certain characters. For example, Drobot's HC requires the player to kill 100 green Chompies while avoiding the purple ones (although you are forgiven if you kill just one). Thing is, there is quite a ton of the purples in the dungeon, and they are also aggressive. Good luck trying to complete this challenge with characters with ranged weapons (you can accidentally shoot a purple off-screen), a wide-ranged attack (the purples will gang up on you), or a Giant (who automatically trample any Chompies that get close).
Any challenge marked "Warning! This can be tough!" has the potential to become this. Like Drobot's challenge above, these often require precision, destroying some targets while avoiding others; and some Skylanders are just no good at avoiding collateral damage.
Ugly Cute: About half the skylanders. Kaos and Glumshanks may also count.
In-Universe, the Wilikin are a race of wooden doll people who creep out almost everyone who interacts with them.
Viewer Gender Confusion: If you never read her bio, you might be forgiven for thinking Sonic Boom is male in the first game, despite the focus on using her eggs/hatchlings in combat. In Giants however, she's given a clearly feminine voice.
The Woobie: Sonic Boom. She went to hell and back to find a safe place to have her eggs and some rotten wizard decides to put a curse on them so they always return to their eggs after a short period, meaning she'll never see her babies get to grow up. This didn't stop her from teaching them to kick butt, however.
You have to feel a little bad for Night Shift as well. He got banned from boxing, his favorite sport, all because there was a change in rules which outlawed teleportation. It's implied that he has no control over his abilities.