A lot has been said about the low difficulty of the Pokémon series in recent years, especially as the first generation of games could be brutally hard, depending on the player's choice of starter Pokémon.
All of the mainline Pokémon video games start with the player choosing or receiving a Pokémon. In most cases, the player chooses between a Grass-type, Fire-type, or Water-type Pokémon. The starter Pokémon will be a staunch ally throughout the game, and most players will keep them on their team until the end of the story. There is a certain feeling of accomplishment of taking a tiny Pokémon, evolving it into a massive beast, and using it to overthrow the Champion.
In Pokémon Red & Blue, the player had to choose between Bulbasaur, Squirtle, or Charmander. The people who were playing the games back when they were first released didn't realize the gravity of this choice, as the starter Pokémon acted as a difficulty mode for the early hours of the game.
The Rock Wall Of Brock
The early opponents in Pokémon Red & Blue are the rival, the enemy trainers between Pallet Town and Pewter City, and lots of low-level wild Pokémon. The first major obstacle that the player needs to overcome is Brock, the leader of the Pewter City Gym. Brock specializes in Rock-type Pokémon, which means that Bulbasaur and Squirtle will steamroll his team with moves that have a type advantage. Charmander lacks any moves that are effective against Brock's Geodude and Onix, which can prevent the player from progressing without a lot of grinding.
The modern Pokémon games can easily connect to the Internet, which means that it doesn't take much work to find a Pokémon of a specific type. If a Dragon-type trainer is giving a player grief, then they can go online and seek out a Fairy-type Pokémon. Pokémon Red & Blue didn't have this feature, which meant that players were restricted to whatever wild Pokémon were available in the game. This meant that the Charmander players had to make do with what was available at the start of the game.
The best anti-Brock weapons in Pokémon Red & Blue were Butterfree, the two Nidoran, and Mankey (which is Pokémon Blue exclusive). Butterfree can learn Confusion, the Nidoran can learn Double Kick, and Mankey can learn Low Kick. All of these moves require a lot of grinding from low-level foes to learn, which can be an exhausting process, especially as Viridian Forest is filled with so many enemies that use status effect moves. Charmander players had a hard time with Brock, but the worst was yet to come.
The Wrath Of Misty's Starmie
The next major obstacle for Pokémon players is Misty, the Water-type leader of the Cerulean City Gym. Bulbasaur players will likely have evolved their starter into Ivysaur at this point and will steamroll Misty's team. Squirtle/Wartortle players will have a harder time, as they have lost the benefits of a type advantage. Charmander/Charmeleon players will hit another brick wall, as Fire-type Pokémon will be OHKO by Misty's Starmie's Bubblebeam attack.
Fortunately for the Charmander players of the world, there are some potential powerful Pokémon allies that can be caught. They're incredibly rare, but it's possible to catch a Pikachu in Viridian Forest. Route 5 also has a Grass/Poison-type Pokémon for the player to catch, with Oddish appearing in Pokémon Red and Bellsprout in Pokémon Blue. There are also more wild Pokémon and trainers around for the player to grind for experience points, so the process of leveling isn't as frustrating.
Once Misty is defeated, things become easier for the Charmander players. The Gym Leaders aren't as brutal and the player has more options for catching Pokémon and grinding them for levels. The old school Pokémon fans might complain about how easy the modern games are, but that's because they remember the struggles of taking their Charmander all of the way to the top.