Eelektross talks about Generation 1 (bcoz sleep is for chumps)

Firstly, I'd like to mention the overpoweredness of Psychic. If you want a textbook example of horrible element imbalance in an RPG, look no further. What's worse is that Ghost, which was supposed to counteract Psychic, could not affect Psychic at all due to a programming error. Later on, they fixed this with the introduction of the Dark type. And now Psychic is hands-down the worst element. But that's not the point. The point is that they made Psychic too damn powerful. Even if Ghost was supereffective against Psychic, there was only one Ghost pokemon family (Gastly-Haunter-Gengar), so Psychics would be just as rampant (and Gengar would probably reach the Top 10 in usage charts)

Secondly, some design elements were horrible. The HMs' only purpose was to check if you had X number of badges. Not only was this annoying, it didn't work. I think there's a guide somewhere on how to skip to Blaine after fighting Misty. This proves that for all their preventive measures, you could still bypass gyms. 

Lastly, even ignoring Psychic's omnipresence, type matchups were horrible and imbalanced. Fire didn't resist Ice, for example. They...yeah, type matchups were horrible and buggy. 

To be fair, this was the first game in the series. They were bound to make some mistakes. Still doesn't excuse some of the stupidity (like Psychic domination) though.

For all its flaws, here's one thing Gen 1 did the best in my opinion: immersion. From the moment that you spawn in your room, you feel a connection to the player that can't be described. When you get your first starter, it's your starter. When your rival beats you, it's you he beat. When you defeat the Elite Four and finally beat your rival once and for all, it's you who whooped Gary's ass and took his place as the Champion. 

This also fits in with the central theme of the game: becoming the best alongside your Pokemon. Your rival is an extension of this. He's designed to give you someone to beat to prove that you're strong: after all, what would a dragonslayer be without dragons? The rival is two-dimensional, yes, but that's beside the point. 

Later games expanded on this: for example, you are now allowed to choose your gender to help with immersing yourself. What I disliked about B/W was they diminished this sense of immersion for the sake of telling a story that, to be honest, wasn't very well-executed. Also, in HGSS your rival was given a backstory which explained why he was such a douchebag, which aided in immersion immensely. You were no longer fighting against a jackass who opposes you for no good reason, you were fighting against a person who was damaged by a bad upbringing and neglect. All in all, I think that R/B/Y couldn't have introduced these two elements better.