These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Pokémon Red and Blue
YMMVs that apply to Red and Blue
Base Breaker: Just like Lyra from HGSS, Leaf suffers from this. Don't get into a conversation on whether or not she exists in the game universe.
Breather Boss: Bruno of the Elite Four can be easily taken out by any decent Psychic type. This was true in later generations as well, but because Psychic Pokemon were no longer Game Breakers players were less likely to have them in their teams.
Creepy Awesome: The infamous Lavender Town theme is absolutely horrifying, and yet so cool at the same time.
Demonic Spiders: Anything that had Wrap and was faster than your Pokémon was this. All the opponent has to do is use Wrap over and over to prevent you from attacking (AI players have infinite power points, you don't). This was especially bad with Tentacool and Tentacruel, who could couple it with Poison Sting, doing more damage and potentially losing a Pokémon.
Fandom Berserk Button: Do NOT call Red "Ash" on a Pokemon forum. It will not be pretty. Not helped by Nintendo calling the trainer and the rival with the same names from the anime, before they got the names of Red and Green/Blue in Generation II.
Unfortunately, this phenomenon has also produced a similar Fan Dumb with the opposite agenda; these fans are quick to label anyone who prefers or emphasizes Gen I and/or II as a rabid Genwunner, even if they do enjoy other generations.
The Psychic Type. On top of being an Infinity+1 Element, as it only deals half damage to itself and is only weak to the underpowered Bug type, every Psychic Pokémon has access to the move "Psychic", one of the strongest attacks in the game. Psychic attacks are classified as "Special", which go off the user's and the target's Special stat. The move Psychic is not only very strong, it has a 30% chance of lowering the opponent's Special stat, making it even stronger. If used with Amnesia, which increases the Special multiplier by 1 with each use, Psychic Pokémon go from overpowered to nearly unstoppable.
The item duplication glitch in Red & Blue, which makes the game obscenely easy if used on items like Master Balls and Rare Candies (as it nearly always was). It can also be used to allow one to catch Safari Zone Pokemon the normal way. Fixed in Yellow and the remakes.
The Toxic + Leech Seed combo. For some reason, when used together, Leech Seed starts dealing escalating damage, just like Toxic, with the healing effect amplified proportionally.
High critical hit ratio moves almost always deal critical hits in Gen 1. Critical Hits in Gen 1 are based on the Pokémon's Base Speed Stat, with high critical hit ratio moves being 8 times more likely. This means that anything slower than a Goldeen may not critical hit with one. And while that does include 66 different Pokémon, the majority of them are not fully evolved and so they don't get used much. Even the slowest Pokémon in the game (Slowpoke) will still get a critical hit more often in Generation 1 than in any subsequent generation.
Catching one of the glitch pokemon (M, Missingno, whatever one appears depending on the name you entered) will allow you to level up to around lvl255 making any battle into a Curb-Stomp Battle.
Genius Bonus: The Magikarp line is a reference to a Chinese legend that states that if a carp can jump over the Dragon Gate (believed to be at the top of various waterfalls), it will be transformed into a dragon as a reward. This holds more ground when Pokémon Snap shows a Magikarp jumping into a waterfall and emerging as a Gyarados.
Growing the Beard: Pokemon Yellow actually is a better game than Red and Blue in terms of gameplay, as the majority of bugs, glitches, and imbalances are fixed, and the way is paved for the full beard-growing of the franchise with Gold and Silver.
Good Bad Bugs: Missingno., M, Glitch City, the Safari Zone glitch, and the Mew glitch, and many other bugs can easily be exploited by the player. These games push the Game Boy cartridges to their limit, and the majority of the more famous glitches stem from shortcuts the programmers took in order to be able to fit the game within the relatively tiny amount of memory available. The Missingno. and Glitch City bugs are the result of the games having no actual memory protection, so the game tries to create a Pokémon encounter or environment from the wrong sets of data with no fail safe to notice the difference. As a result, it's possible to break the game to ridiculous extremes and still have it keep on trucking through everything. Additionally, a bug lets Psychic Pokémon be super-effective against Ghost instead of being completely ineffective (all Ghosts in Gen I are also part Poison). This makes Ghost Pokémon rather weak but Psychic Pokémon (like Mewtwo) awesome.
Harsher in Hindsight: In the Pewter City Museum, there is a model of the Space Shuttle Columbia, which disintegrated in 2003. While it's still explicitly referred to as such in the Japanese version of the remakes (since the Japanese versions were released before the accident happened), in the English version, it's simply referred to as "Space Shuttle."
A Lass outside of the Rock Tunnel complains that there should be a pink Pokémon with a floral print. Now that Black and White are out... Given the reported number of unused designs for Pokémon, many which got used later, it could easily have been an In Joke at the time.
One of the little quirks of the Missingno. glitch is that, due to not having a back sprite, he'll appear as the last pokémon loaded into memory. This later became Zorua and Zoroark'ssignature power - they'll appear as the last pokémon in the team.
Seinfeld Is Unfunny: The games are certainly starting to show their age. Ugly sprites, slow pacing, a primitive battle system and the sheer amount of bugs are certainly unimpressive to players who played the later games first.
Sabrina. Psychic types are gods in this generation, so naturally...
Lance, the fourth member of the Elite 4. Four of his Pokémon are Dragon type, which are only vulnerable to Ice and Dragon, and resistant to all fournote Grass, Water, Fire, Electric (in Yellow) starter types. As this is the first (and only) time that particular type is fought in the single-player game, it is entirely likely that the player doesn't have an Ice-type Pokémon or move prepared, nor is there a Dragon-type move that can be used against them — the only Dragon-type move in the game, Dragon Rage, deals a fixed 40 points of damage, and ignores type.
Unfortunate Implications: Upon arriving in the US, Jynx caught some flak for being a blackface caricature (the intention may have been a ganguro instead, but we're not sure). Its skin was changed from black to purple in later games to avoid problems.
Prof. Oak. came when he heard Blue beat the Pokémon League.
Ekans = snake, Arbok = cobra, Muk = ???
Alternate Character Interpretation: In one "interpretation", your rival is the good guy. note In Lavender Town, he asks you "What brings you here? Is your Pokémon dead?" before challenging you, without explaining what he's doing there. You then fight him, and if you've been paying attention, you will notice that he no longer has a Raticate. The theory is that the player character wounded their rival's Raticate so severely that it died of its injuries, spurring him on to beat the Elite Four before the player. But shortly after he has defeated the Elite Four, he must fight the player...who defeats him...and then is congratulated by none other than his grandfather, Professor Oak, who scolds Blue and claims he lost because he did not treat his Pokémon with love and trust. This gives the fairly one-dimensional rival character a deep story and portrays him as a tragic hero with terrible luck. It also makes your character's actions fairly despicable, as all this guy wanted was to be a great Pokémon trainer and win his grandfather's love. Easy to poke holes through this. This does require some big assumptions, though, and doesn't change the fact that he acts like a Jerkass towards you.
Professor Oak has had a few theories devised about him over the years. The first type of theory is that he's a Genius Ditz who understands Pokémon but is too stupid to keep all the data about them, hence why you have to recollect all of it. The second kind of theory puts him in a somewhat more malevolent light, either as having some illegal ties to the various villain teams or as the Bigger Bad of the franchise.
Pokémon Origins went out of the way to debunk both of these: Blue really is an asshole, but not an irredeemable one. Oak is even called out on sending the two of them out: his response is that both of them have major flaws that this adventure might help them grow out of. He wants Blue to learn compassion and stop being the resident Jerkass and for Red to stop pussyfooting around and Dare to Be Badass. The adventure proves him right: Red becomes one of the most famous badasses in Pokemon history and Blue's defeat at this hand leads to his softening by the time of Pokémon Gold and Silver. History proved him right.
Dragonite. It's the original pseudo-legendary, and one of the best Dragon-types in the game... that just happens to look like Barney the Dinosaur. The fact that it bears little resemblance to its serpentine pre-evolutions doesn't help matters. Plus, just like Charizard, all the Genwunner worship it gets annoys some fans of the newer gens. This may be why they gave Iris' Dragonite a grumpy personality and a generally angry expression in the Black and White anime season, to defy its cuddly appearance and help "unify" its popularity.
Pikachu, for all of being the series' mascot, sees a lot of abuse both from people tired of seeing Pokémon everywhere, and from fans who feel it gets far too much attention.
Charizard, despite being one of the most popular Pokémon designs in the series for its dragon-like appearance, is regarded in fandom circles as a symbol for "Genwunners" — people who prefer the first generation over any other, and are often perceived as doing little but complain about later games.
Breather Boss: Giovanni is rather easy for being the final Gym Leader, since most of his Pokémon are rather slow and all of them have common weaknesses, or even double weaknesses. Even more so in FireRed and LeafGreen, where his strongest Pokemon in the original Red and Blue — Rhydon — was replaced by its unevolved version, a Rhyhorn, of all things.
Although most of the original 151 Pokémon have become highly regarded in comparison to later additions over time, and a handful having reached superstar levels, at the time of the release of the first generation several Pokémon in particular stood out apart from the starters and Pikachu:
Mewtwo, the strongest Pokémon in the game. It is caught at level 70, has a sleek, alien look to it, and outclasses every other Pokémon in the game in pretty much every way.
Alakazam is one of the strongest Pokémon in the game, as it is Psychic, has an excellent moveset and great stats. It is often replaced by Mewtwo, which is better in almost every way, but by the time the player gets that far, Alakazam will have been in the player's party for most of the game. As a result it is very fondly remembered.
Gengar is a nasty-looking Ghost-type Pokémon with excellent stats and a cool, creepy moveset. As its evolutionary line is the only set of Ghost-type Pokémon in the game, its immunity to Fighting- and Normal-type moves also helped set it apart. This is particularly noteworthy for the originals, as Ghost-type moves didn't work on Psychic Pokémon owing to a case of Good Bad Bugs.
Scyther is a ninjaesque version of a praying mantis, with its scythes being actual metal blades. Thanks to its badass appearance, it quickly became a fan favourite, despite its rarity.
Eevee and its "Eeveelutions" became highly popular for two reasons: first, allowing more than one evolution was a mechanic unique to Eevee at the time, and second, the Eevee-related Pokémon are one and all considered to be adorable.
Gyarados is one of the most physically intimidating Pokémon in the generation, being an enormous, very angry-looking sea dragon. Having come from the incredibly weak Magikarp makes it particularly memorable.
First Installment Wins: The first games, and the original 150 (+1) Pokemon are pretty much synonymous with the series. The starters are always compared to Charmander, Bulbasaur, and Squirtle, the original 150 typically dominate the popularity polls, and Red and Blue/Green/Oak are the most well known Protagonist and Rival respectively. Despite all the glitches, general messiness and "Genwunner" backlash, there's little doubt that the originals are the most well-remembered and generally liked among fans both new and old (mostly due to the Pokémon fad at the time of Red/Blue's release, and the fact that it's more common to find fans of newer gens who are accepting of older 'Mons than the other way around).
The Scrappy: Mr. Mime and Jynx are widely disliked by the fandom for their disturbing designs. Fans of the newer gens also tend to criticize Gen I Pokémon with overly simplistic designs such as Diglett, Magnemite and Grimer (though evolutions introduced in later gens such as Magnezone tend to alleviate this somewhat).
The Woobie: Cubone. You would be too if your mother died after you were born, you couldn't look at the moon because you could see her face in it, and you had to wear her skull to hide your face.