For those who played non-portable Nintendo games before 2008, there is little need for an introduction to the Smash Bros. franchise, because you already know all about it. For everyone else, an introduction would be extremely hard because the game's concept sounds very strange. It is a fighting game, but there is no health bar. There's a meter showing how much damage you've taken but it counts up, and the meaning of the number varies from character to character and from situation to situation. And you do a lot of platform-style jumping. It's not much of a description, admittedly.
The most telling thing about Smash Bros. is that when a new Nintendo comes out with a new console, nobody wonders too long on what they're going to do in that generation's Smash Bros. Everyone knows what they're going to do: they;re going to sharpen the existing mechanics, they're going to add new characters and stages, and it's going to be great. Rarely do players say, "They've done this before," because it doesn't matter. They have done it before; and it's still great. Everyone has their favorite game of the three, but that comes down to preference.
And of course any series whose games are broken down by mere preference will usually have a very solid core of game design concepts working for them.
Smash Bros. is not just a fighting game; it is also a platformer. This is apparent on some stages more than others (all the Metroid and F Zero stages, for certain), but platforming elements are an inextricable part of the game';s design and mechanics. The defining thing about this design idea, however, is that platforming fits into the fighting game controls very intuitively. The way the platforming fits into strategic positioning in combat is more complex, but players will almost never say "I really need to work on my platforming skills." They will quickly get a handle on the combination of skills.
But even in stages that are not dynamic at all, the mere presence of platforms changes the combat strategy entirely. There are characters against whom you do not want to be caught on a high platform: Jigglypuff, Marth, Sheik, because their ability to juggle your fighter is only increased. Then there are characters against whom platforms and platform-style jumping are an aid because they can mitigate projectiles well: Samus, Lucas, Lucario.
And since the victory conditions in most game-types involve knocking everyone else off the stage, platforming skills will make spiking flying enemies down into an abyss, or recovering from such an attack an intense part of combat.
Smash Bros. is a great example of a character balance that takes place across a large number of statistical categories. Most fighting games achieve their character balance through a few but extremely complexly executed number of attributes in their characters: attack range, attack priority, character and attack speed, and raw damage output. Smash Bros., because of its genre composite, is able to add more.
Character Weight - affects amount of damage that can be taken before being knocked off the stage for a KO, among other things
Character Fall Speed - greatly affects strategy in air combat
Projectile Priority - surprisingly robust system
Air Priority - this exists elsewhere but is only used extensively in SB
Optimum Range - many characters have an ideal range at which they do the most damage with their smashes (Roy, Marth, Falco)
Charge Time - many attacks, especially smashes and projectiles, have a charge time with its own unique powerup/growth curve, to be observed for tactical usage.
Many of the implementations of these stats are so subtle and intuitive that players will find themselves using the attributes of their characters without thinking about it. All they know is that a certain character really matches their play-style, and that they bring the most of that character. That, of course, is great fighting game design in action.
In many fighting games, the fighting stage is simply a backdrop, adjustable without any real consequence. This was never true in Smash Bros., where every level has always been significantly different from every other. Beyond being just different sets of terrain, however, the stages are actually quite active in their contributions to battle.
Starting with the series second installment, Melee, a large number of the multiplayer stages became completely dynamic. Some of the stages are constantly moving their ring-out boundaries, like Rainbow Cruise and Rumble Falls. Some of them are made up perilous moving platforms, like the F Zero stages and Poke Floats. Some of the stages have destructible terrain that regenerates (Mushroom Kingdom, Skyworld) several times during a match. Some stages are actually several stages in one, transforming into a number of very different terrain shapes. And with the latest installment, some of the stages (Halberd) will even fire lasers directly at the player characters.
In short, there is no such thing as a "normal match." On the other hand, however, it's also rare that players will complain that a certain stage gives preferential treatment to a specific character. Or at least the complaints are so diffuse among character/stage combinations that we can conclude it's personal preference.
Smash Bros. changed the way that we look at fighting games, from a design perspective. Unfortunately the series has been so effective at executing an alternative fighting game that it’s hard to learn anything from it. What about Smash Bros. could you imitate without your game becoming Smash Bros? Certainly the removal of the standard health bar is a feature worth imitation; but the ring-out system seems like its only obvious end. Platforming and fighting work very well together too, but the only alternative to what Smash Bros. has done would seem to be a 3D version of a platforming fighter. At that point you’d have something very close to an action game, although Dissidia has done a little of this with some success; their starting point, however, was very different. In any case, Smash Bros. will remain a landmark in the genre that continues to peerlessly innovate.