Megaman Legends

For most people, this is considered the Black Sheep of the Megaman Family. But if they shyed away from it because of the vast differences for the more normal Megaman games, they missed out on a Great Title.

While it did away with the whole Eight Robot Masters Formula, it went for a much more customizeable experience. You can find parts to upgrade your Megabuster, increasing its Range, Power, Speed, etc. You also find Blueprints for other special weapons and must actually go out and explore the mines to find the parts to make and upgrade them.

So while it is a castly different experience from pretty much every other Megaman game in existance, it is definetly worth a play through, you won't be disappointed.