Unchallenging, bland, and unstimulating, despite the ambitious concept.
Cons - Battles are ridiculously easy even against much higher level opponents, opponent AI is terrible, plot and characters are shallow and uninteresting, gameplay and battles are repetitive and redundant, each copy of game has only 1 save file
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Growing up in the 90s and early 2000s, you'd have had to be living in a cave to have not at least heard of Pokemon, and it was this game that started the whole craze, including the once-vastly popular trading card game, and the terrible cartoon series which is apparently still on the air.
There's no denying that Pokemon Red/Blue was an ambitious game, and has a much larger depth of content than virtually any other Game Boy game of the area - with numerous Pokemon to collect, numerous moves to learn, and the concept of linking your game with those of friends or siblings to do battle, or trade Pokemon with the ultimate goal of "catching em all".
However when it really boils down to it, the core gameplay design is what really makes or breaks the game, not all the bells and whistles - and this is where this game really falls short, regardless of what fond childhood memories you have with it.
As fun as it may be to discover and catch new Pokemon, the actual battles are absurdly easy - primarily because of the "rock/paper/scissors" style combat system (ex. Water pokemon beat Fire Pokemon, Fire beat Grass, etc). Matching the correct type of Pokemon or attack to your opponent's Pokemon seems to make way more difference in who wins than the actual levels of the Pokemon. For example, your Pokemon could be 10-15 levels lower than your opponents, but if your Pokemon has the advantage in "type" (ex. You're using Fire, he's using Grass), then you'll be able to 1 hit KO all his Pokemon without taking a scratch.
Seeing as I haven't played this game in years, the other day I watched part of a video walkthrough of Pokemon Red on Youtube just to recap some of my old memories, and it is pretty much just as I described. The player was actually up against the game's equivalent of the "final bosses", and his Pokemon were all 10-15 levels lower - however he was able to KO all of their Pokemon without losing a single one of his, just by matching up the right Pokemon and attack types to their - and these were the "final bosses" too, not just some run-of-the-mill opponent either. In conclusion, once you've learned what each Pokemon type is weak or strong against, there's virtually no challenge whatsoever - and battles are just a matter of redundantly issuing the same commands over and over, with little to no challenge or suspense.
To top that off, the AI of opponents is pretty strikingly bad, Sometimes you'll see an oppenent with full HP use a heal move, which does nothing more than waste a turn. Other times your Pokemon may only a few HP away from "fainting", and your opponent will waste a turn (or several turns) using a move that lowers your defense, when any attack they could use would knock you out even with full defense. Though even if the AI was perfect it wouldn't make this game any less of a walk in the park - so these flaws are just icing on the cake.
Even if an RPG's gameplay leaves something to be desired, it can make up for this if it has a deep plot, well-written dialogue, and memorable characters. However Pokemon Red/Blue has none of these either - the plot boils down to the main character traveling around the world, pitting his Pokemon in battle against several "Gym Leaders" in an attempt to collect 8 Badges needed to enter the a Pokemon League tournament, where he'll face off against elite trainers, and eventually his childhood rival for the title of Pokemon League champion - the plot's enough to get the game going, but is nothing special or truly memorable. and all the characters in the game are flat and generic with little to no personality or reason to care about them - you'll encounter various NPC characters in the many towns and villages you pass through, but few if any of them have anything interesting to say - so the plot and characters end up being as flat as the game-play itself.
Non-combat game-play simply involves navigating around the world, trying to get to the next town to confront the next gym leader, while running into battles with wild Pokemon or other trainers in between - it's more or less what you'd expect from an RPG and doesn't stand out in any way.
It's also worth pointing out that each copy of Pokemon Red/Blue only allows you to have 1 save file at a time, my theory is that this was an intentional design choice by Nintendo, meant to motivate parents to buy additional copies of the game for each of their children, since siblings wouldn't be able to each save their own game on the same cartridge. And I have to call Nintendo out for this screw-up too.
The most interesting and memorable part of Pokemon is the diversity of different Pokemon, and finding and catching every last one of them, and the ability to face your Pokemon off against a buddy's. However despite these truly innovate concepts, and the fun memories you may have had of facing your Blastoise off against your brother's Charizard - it's not enough to save this game from it's "walk-in-the park" easy battles and sheer blandness and redundancy of core gameplay. If you loved this game as a child, just remember that a lot of us loved Barney the Dinosaur as an even younger child too - 90% of your fond memories are coming from pure nostalgia, not anything about the game itself, trust me.