Rattata is for many people one of the most frequent early-rodent-type Pokémon in the entire franchise, but not as annoying as the derpy Bidoof and the intimidating Patrat. Some may find it still quite annoying though.
This is the favorite Pokémon of Youngster Joey (the one from Johto, at least). If you register him on your PokéGear, he'll occasionally call you to gush about his "top-percentage" Rattata again, whether it's still a Rattata or it has evolved into Raticate. This is what many players remember the most about Rattata.
Rattata is actually the only early-Rodent Pokémon who isn't Brown or has no brown in its coat (which is funny because he is the first one). Rattata's coat is purple, which is, by the way, still a quite unusual color for a Normal type mammal (I mean what other Normal mammal Pokémon is purple? Delcatty?) However, Rattata's evolution Raticate actually turns into a bright brown color.