The "Overloaded" character kit, is what defines League of Legends.

The characters of a character based game; MOBA, fighting, or otherwise, obviously holds a lot of weight. but it is how Riot goes about defining these characters that makes League of Legends something special compared to others.  Certainly limited by many of the game's mechanics, we are going to be talking about how many characters break those limits rather by defined by them, and in that brokenness we find the secret.

First, understand that League of Legends had carved itself out of DOTA but shaped itself as a wholly different game.  DOTA character kits are rather complex descriptively but simple mechanically and visually because of its item shop which is grossly more active oriented compared to League of Legends.  This void was filled directly with the characters in LoL so from the start, we had "Overloaded" kits just to a much smaller less original degree than we do now.

A few of the many stand out characters among the League of Legends roster;

These handful of Champions are all very distinct from other MOBA characters.  Some of them have many defining traits versus any single and that is why many players consider their kits "overloaded" as historically, the MOBA character kits were rather simple especially with the inspiration from DOTA.  Every time Riot releases a new champion or updates an older character, we see their kits becoming ever more complicated and involved.


More Skill Shots
Because simple numbers being added or subtracted is boring and hard to watch.  It is clear to the audience and the players when we have epic tornadoes crossing the screen or laser blasts shooting out. E.G [Yasuo] "has windwall which can block skill shots and has a melee skill shot"

More Passives
Because sometimes a characters active kit is not actually the component that defines them rather the passive traits and then the actives work together with them. E.G [Kalista] "passive radically changes her movement in between auto attacks compared to any other character in the game."

More Mobility
A mechanical based game should strive for an ever increasing skill cap mechanically, and the MOBA genre is very much focused on movement rather than pure aim.  This creates a much more dynamic game.  Mobility is much more visible compared to outplays resulting from hidden math. E.G [Lee Sin] "who's entire kit is defined by him moving in and out of position and doing it often."

More Crowd Control
With such mobility, and a reliance on skill-shots and positioning, CC is required.  However, CC is not an answer to a problem but the final ingredient in a formula for an awesome viewing experience and a challenging competitive atmosphere.  E.G [Gnar] "having multiple forms of AOE CC in the form of skill shots and abilities that interact with the environment itself making player positioning just as important as enemy awareness"

In the end, its not like a complex character is better than an older champion, see [Annie] vs [Ahri] but more that the playstyle for one character is more often stagnant compared to other and in a competitive environment, you want anything but stagnancy.

A passive, three active abilities, and an ultimate active ability.  These have been broken by adding passives inside of active abilities, or making actives toggles.  Some characters even have toggle forms which allow them to effectively have 6 or more abilities.  Other characters even get unique items and who knows what next will be invented.  These rules are made to be broken because League of Legends itself is in a genre that was previously known as having very strict rules, and LoL has grown to what it is today because it set out to change that.  So as time goes on, it must and will expand and become more overloaded as some would call it, but it won't ever be diluted.  We can trust Riot to ever be expanding in new ways to interact in the game.

Different Kinds of Skill Shots!
Bolts, Blasts, Waves, Stabs, Swings, Chains
League felt much more mechanical compared to DOTA, so it made sense to have fighting style abilities and combos which required melee range aimed skills. [Riven]

Different Kings of Passives!
boons, debuffs, entirely new stats, new resources, hidden situation actives
A separate passive skill was new for LoL and with this comes new territory to expand kits situationally such as the ability to create towers out of tower ruins. [Azir]

Different Kinds of Mobility!
Leaps, Blinks, Entity Based Dashes, Terrain Based Movement
Bushes were unique to League of Legends, they put a character that could leap if he was standing in a bush next to an enemy [Rengar]

Different Kinds of CC!
Knock up, Knock back, Fear, Pull
DOTA is known for having huge CC timers but League has many/varied CC instead, so a character kit focused on crowd control would need control that could be stacked and used together or separate for optimum results depending on the situation. [Thresh]

Complexity in a kit does not always beat out raw stats, and complexity is not always more fun to watch, but the direction Riot is taking LoL is not pure complexity with their characters but rather reworking strategic diversity and translating that potential into more spectacular and visceral mechanics.  To make something new mechanically and to always differentiate itself from more strategic competitors, League of Legends has some regulations to simplify certain game-play elements and what is fun about these character kits is that often they are inspired by the very breaking those rules; this gives League an overall very understandable and watchable game flow, but potentially infinitely deep game-play.