1st Gen One thing from the future.

[Seki]

The box system! If your box was full, it wouldn't allow you to catch the Pokemon. It was tedious to remember to change the box, and for a kid, you don't think of things like that until you're trying to capture a legendary. That is what I would change, and it would have made things much more easier.

This. And the bag, seriously, why does the bag has so limited space!?!

 

[0xTidusx0]

Less ridiculous-childish looking pokémon would do.

 

[TehFisharmahn]

I would remove or add nothing. I'd improve AI. Really. Fighting a Gengar vs Lance's Dragonair? He would use Agility and nothing else, because it's type is Psychic.

 

[Roh]

A bag with organized pockets.

 

[DothThouEvenHoist?]

I'd either add Shiny Pokemon, or the ability to run with the Running Shoes.

 

[PuzzledPsyduck]

I know younger me would have loved to be able to rebattle almost everyone in the game like in Gold/Silver. After a certain point there isn't really anyone to fight except the Elite Four repeatedly.

 

[takeKopter]

move relearner. some higher level Pokemon like legendaries missed a lot of move, and you cannot get the move you want. even trading to G/S and breeding is not a solution because, well, they are legendaries..

 

[lmcde22]

A bag with actual pockets... I would even think about unlimited bag space like in Gen V. But it was ridiculous in RBY. There was no room for anything. It was all taken up with Key Items (like Map and Silph Scope and Fishing Rod) and the HMs took up space too. Ugh.

 

[tranceking26]

carry more/all items, I had to store all the TM/HM in the PC

the pack upgrade in GEN II was much appreciated by me!

 

[Noka]

Ooh, tough question, but in the end I think I'd have to saaaay...

Unique evolutions. Like how Eevee can only evolve into Leafeon at the Moss Rock.

 

[BlueMudkipz]

oh god, the possiblities. In RBY i would add the Day Night cycle. Athet did a phenomenal job of it in GSC and i would have really enjoyed it in RBY ~blu

 

[Psychic-X]

I'd have to add Running Shoes. I found it very tedious to play the first Gen games because of the absence of Running Shoes.

 

[Sean.]

Tucker.
The sexalicious Frontier Brain.

 

[classiccartoonsftw]

If I could make only one change, I would bring the type chart from GSC into RBY.

 

[Charizard17]

More Dragon-type moves, as there was only dragon rage back then, that always dealt 40 HP damage.

 

[Sirfetch’d]

I'd add breeding in the games. Ever since breeding was introduced it has been a staple of the games and I think would make the originals really cool!

 

[Biblioteca13]

An online trading system :D

 

[ErikaInRainbowCity]

I think the Dark and Steel types would have made the games more interesting if they were put in :)

 

[BubbleBeams]

Oh man definitely separate compartments in the bag. Besides the fact that you can't carry very much in the bag anyway, the lack of organization makes me batty.

 

[Lucky1Yena]

I would either add rematches with trainers, or a Battle Frontier like in all games past Emerald.