Pokemon HeartGold and SoulSilver
The original games surprised everyone by including the entire Kanto region from Red and Blue, allowing players to face off against all eight Gym leaders and eventually battle Red on Mt. Silver. This was on top of having to collect 493 Pokemon but the remakes also add the Battle Frontier with additional battles culminating in boss fights with Frontier Brains. Certain Pokemon are also not allowed, increasing the challenge involved. Completing certain side quests also lets you obtain Ho-Oh and Lugia, the two new Legendary Pokemon.