I'll make a more straightforward query to everyone in the thread since I'm interested: what would be two games you consider definitively simple, two games that you consider borderline, and two games you consider overtly complex?
In my honest opinion:
(Incredibly) Simple:
- Pong, Flappy Bird and other similar casual games with no complex mechanics driving them
Borderline (?):
- Games that are simple to play, but at the same time are driven by more complex gameplay mechanism which do not require player participation, for example racing games that are not simulations
Complex:
- Games with a complex gameplay mechanism that requires player participation in order to play them, for example Baldur's Gate, Fallout and most RPG's
Here's my reasoning. Pong and Flappy Bird are both incredibly simple games with a very simple premise and very simple mechanics driving them, they're the epitome of what I would consider
"simple", or even minimalist. They best illustrate what I understand as simplicity - there is practically no learning curve because everything required to play them is presented to the player in a straight-forward way and there are no in-depth gameplay mechanics for one to consider. This simplicity can be extended onwards to
"more complex" games like SHUMPs, the general idea is that if the game has no complex mechanisms that require mastering to actually play the game effectively, they're simple.
I would probably say that a borderline game is a game which is simple to pick up, however the mechanics that drive it may be pretty complex, require a degree of mastery
(or the mythical "skill"), however they work in the background and do not require active player participation in order to function - they are taught by experience rather than by necessity. Most racing games could be put in this category - you are presented with a simple control scheme for controlling the vehicle, however in the background, there's a physics engine that controls most elements of your gameplay. Impact into a boundry at high speed is going to have more drastic effects than impact at low speed, cutting corners can allow you to get ahead of your opponents despite driving at a lower speed, utilizing drifting may allow you to cut those corners at a higher speed than it would normally be possible etc. The forementioned Smash fits neatly into this category simply because it contains physics, and this inclusion requires the player to strategize gameplay on the basis of the damage levels, the available skill set of the characters used etc.. In conclusion, a borderline game would be one that's very simple to pick up and play, but still designed with a somewhat complex system underneath the hood, a system about which the player is often completely unaware, but nevertheless a system that requires a degree of mastery.
Complex games are games based on a system of variables known to the player that directly impact gameplay in such a way that not knowing them would be detrimental to the player or in extreme cases it would actually stall the game. In the case of Baldur's Gate, this set of rules is directly based on D&D which is insanely complex on-paper and features such wonders like the
"Conga Line of Death" as described by Spoony according to which attacks from various directions cause a varied degree of damage on top of the obvious matters such as a skill tree, a stats system and other customizable and non-customizable elements of the mechanics. In some RPG's, it doesn't matter if you're holding a mace, a dagger or a sword - you're just doing X amount of damage and that's that. In D&D, you have to consider the amount of dice a given weapon uses to generate damage which can give you better or worse prospects
(in other words, maximum damage does not always directly translate to maximum DPS), the type of weapon
(two-handed, one-handed, double-weapon, dual wield etc.), the type of damage it deals
(blunt, slashing, piercing etc.) and the type of your enemy and its defensive capabilities against said weapon. In the case of Fallout, the system used is called SPECIAL and it has seen a revival as of late in games like Fallout 3, Fallout: New Vegas and even Skyrim, in a modified way. In SPECIAL, the character's talents are represented in percentages which simplifies matters at face value, but the underlying mechanisms are still as complex as D&D, if not more so. In both later D&D and SPECIAL the direction the hits are coming from is not the sole determining factor of damage - you have to consider individual body parts of the enemy as well as the possibility that you might be able to deal a crippling strike... or receive one yourself, which can change the outcome of the battle substantially. Of course such complexity isn't limited to role-playing games - many shooters implement similar mechanics, cue the inevitable headshot reference. In short, by complexity I understand the degree of knowledge required to not just play the game, but to play it effectively. The more the game plays out in your head rather than in the actual game the more complex it is.
tl;dr I think I simply draw the lines between the three on the basis of gameplay mechanics. Games which do not feature a complicated gameplay mechanism of any kind and are presented in a simple fashion are simple, games that do feature such a mechanism, however said mechanism is in the background and does not require the player to actively participate in it are somewhere in-between, while games that require the player to utilize said mechanism and knowledge about it is absolutely crucial to gameplay are complex. Of course this is all purely theoretical - there are other matters that have to be considered, such as the actual complexity of the presented mechanism, the intentions of the developers, the way actual gameplay in played out and so on. It's all a very individual matter, I think.
You cannot have a good "high and low" system in smash because in order to execute special attacks you use all 4 directions comboed with the action button. Well I suppose theoretically you could, if you made all the down+A actions be recognized as low-hitting ones, but that would be extremely limited as each character would have a single low move and a single high move, it would be close to pointless in the way smash works.
I think the biggest problem here would be the actual size of in-game models on the screen. I think the designers forfeit the idea of including the High/Mid/Low distinction in Smash simply because actually seeing what's going on on-screen is often a challenge and it wouldn't necessarily help players gain the edge, rather it would introduce a degree of randomness, if not chaos to the gameplay. knock-back trajectories are not an equivalent substitute in Smash, but they serve the game well and replacing them with something else would probably make Smash less Smashing - a joke to lighten up the atmosphere.