Aspiring entomologist Satoshi Tajiri was desperate to make a game that paid tribute to his passion for bug-collecting, and with artist Ken Sugimori this ambition would begin to materialize: Implemented with the growth and evolution of some animals (IE how the tadpole "evolves" into the frog) and the novelty of the Gashapon capsule machines, the conceptual base of "Capsule Monsters" would be conceived to become "Pocket Monsters" until finally "Pokemon" in versions Green, Red, and Blue in 1996.
You know the rest of the story: a variety of updates have been made to the series ever since; but in truth, despite all the generational changes Pokemon's original 1996 releases are experientially no different to play than any of the series' sequels because the gist of the design has yet to change -- you compile creatures to use as weapons (specified with individual stats and health), then you work to advance these stats so you can defeat everyone else's creatures (their "weapons") to your heart's content. The system of parties leveling up per member wasn't a revolutionary idea, but the game worked with it in a compelling way: there is a discernible amount of effort put into making every "pocket monster" endearing and memorable in aesthetic. It is indeed difficult to regard your creatures as mere "weapons" when you hear their distinctive names, physiognomy, and roars each time you pull them out -- and this is even before players would see any of the franchise's anime series, card games, movies, or comics that chiefly exist to characterize all the Pokemon and the world of the franchise.
The central joy derived from the game isn't beating your opponents; it is playing the role of coach for your creatures to push them forward bit by bit, seeing them advance in every area of their stats. Yet due to the game's ritualistic nature of "training" your creatures (grinding points in multiple battles), the gameplay can get tedious if you lack a certain level of patience -- playing through the same song and dance of turn-based combat filled with redundant text and pitiful pixel animations, or running through the identical forests and hiking trails to the next town, or reading the dryly written dialogue and narrations that portray a barely comprehensible story... it's as "fun" as it sounds.
Although I admit that the vagueness of the story actually works for such a repetitive and open game because it leaves a lot of space in the plot for the player to fill in with their imagination. I myself would start to daydream in the process of grinding Exp in the wilderness, wondering what it would exactly look like for a Snorlax to tackle a Caterpie into a slightly frazzled state of unconsciousness, when realistically such a tactic would result in the little insect's smooshed guts smeared all over Snorlax's belly fat.
There is scarce variety in the trainers you fight, which makes the gym leaders (who act as "bosses") and the scripted confrontations with Team Rocket or your "rival" somewhat refreshing in the midst of what would have been another predictably banal area to run through. And at least there are attempts at variety in the townsfolk: half the time you interact with them their response is perhaps a useful hint or a sudden gift that you needed to progress, yet most of the time it is irreverent information to waste your time.
One more feat of Pokemon was how you could trade your critters with other players, but this was mainly done just to obtain the evolutions of Pokemon that required you to do this.
Consistent with the nature of all corporate franchises, Pokemon did not get its jumpstart as a ground-breaking DIA experience in game design -- its pleasures are of light involvement. One "serious" player could plow through the game and manage to successfully "catch 'em all" to the very end, but this would be on the border of unhealthy obsession considering all the games you could play in all that time while in the grip of this one.
The generational sequels innovated as follows:
For the GameBoy Color Pokemon Gold and Silver released in 1999, featuring one hundred new creatures to collect (some of the new types Dark and Steel), new systems of breeding and item-holding, and aside from the obligatory new region to explore, various aesthetic upgrades. (IE a day-and-night time system and an updated color palette.)
The GameBoy Advanced editions were Ruby and Sapphire released in 2002, adding another 135 new creatures, the style of 2v2 battles, and Pokemon contests.
Diamond and Pearl for the DS would release in 2006, expanding the roster of Pokemon by 107, adding Pokemon "Super" Contests, puffin-cooking, wireless battling/trading, and a feature of an app-based watch to use on the touch screen.
The fifth generation was also on DS with Black and White (2010) and their direct sequels Black 2 and White 2 (2012). The two had their own pair of legendaries along with the new 156 Pokemon.
X and Y would release for the 3DS in 2013, with 72 new Pokemon includng the new Fairy type. Other additions: temporary mega-evolutions, some customization of your trainer's appearance, "Super" training, and the battle modes "Sky" "Inverse" and "Horde". Most importantly though, you can move in more than four directions.
Sun and Moon would release on 3DS in 2016, introducing 81 new Pokemon with some old Pokemon redesigned for the Alolan region. With this release the games were becoming more scripted and cinematic, which if handled tastefully could successfully break the monotony that usually tarnishes the Pokemon experience -- sadly, here it was handled not-so-tastefully as your player-character keeps this stagnant zombie-happy facial expression throughout each and every cutscene, no matter the circumstances.
Other notes:
The original Pokemon Green would never get a US release.
Pokemon Yellow, the "enhanced" Special Pikachu Edition of Red and Blue would be released in 1998 in response to the growth in popularity for Pikachu after the Pokemon anime would air its first season in 1997.
Other "enhanced" versions: Pokemon Crystal (for Gold and Silver), Emerald (for Ruby and Sapphire), and Platinum (for Diamond and Pearl).
Remakes of the original games would emerge as Game Freak and Nintendo advanced in technology:
LeafGreen/FireRed (GBA, 2004) <> Red/Blue/Green (GB, 1996)
HeartGold/SoulSilver (DS, 2009) <> Gold/Silver (GBC, 1999)
Omega Ruby/Alpha Sapphire (3DS, 2014) <> Ruby/Sapphire (GBA, 2002)