Satoshi Tajiri's original concept of the worldwide phenomenon, Capsule Monsters was a slightly different beast then the Pokemon we know and love today (or loathe, some of you, admit it).
From much of the information available, it seems that the original concept was something similar to Dragon Warrior Monsters, where a human tames wild monsters, charming them in to following him using Charisma. Capsules were used to house monsters instead of Pokeballs (based on Gashapon, Japanese toy vending machines) (although they are basically the same thing).
Originally the idea was that the trainer would also be involved in battle, but was scrapped because then that would eliminate the need for monsters as protection. This is probably why a few trainers in Red/Blue had whips shown, like Sabrina and the Rocket Grunts.
Instead of Pokemon Centers, trainers/tamers would heal their monsters at the hotel, suggesting a more typical RPG style of game.
The idea of the Pokemart also changed. Instead of being just a place to buy items for your journey, it also seems you could purchase various monsters as well. This would later come to be everyone's favorite scam artist; the Magikarp salesman.
The map of Kanto changed little, beyond routes being named different and whatever the heck that area marked "C" was supposed to be.
A few of the Pokemon we know today were in the original concept art as tamable monsters, including an early concept of Lapras
Ghastly and Slowbro
And even the old rivalry between Nidorino and Gengar got its start here (which as most of us know now is actually a pretty one-sided fight).
Trading between games was still present, although the concept of different versions with exclusive monsters didn't come around until later. Instead it would be encouraged by the presence of ultra-rare monsters, who had incredibly low encounter rates (basically legendaries, but without the rule of only 1 per game).
According to some sources, Gamfreak produced a manga in its early life as a self-published game magazine called Capsule Monsters, but I haven't been able to find any confirmation on it or scans, except for this one panel that honestly scares the crap out of me and looks way too clean a scan for something so obscure from the late 70's/ early 80's.
The name itself wasn't supposed to change, but apparently Tajiri had trouble copyrighting the name Capsule Monsters, so he went with Capumon, and then eventually Pocket Monsters/Pokemon.
So, while we enjoy our shiny new 3D Pokemon games, let's just take a moment to enjoy the work that made it all possible.