2002: The Bohrok were not only awesome and dangerous villains, but also the best canister sets we ever received with a great mix of functions.
2005: 2005 was a common year starting on Saturday of the Gregorian calendar, the 2005th year of the Common Era and Anno Domini designations.
2015: The sets are nothing to sneeze at, but the story is the reason why 2015's so low on the list. That, and 2001 makes this year look like a slow start.
2009: This could've been a whole new beginning to a new big story in Bionicle by introducing us to a new world with new characters and not to mention the awesome, colourful and easily breakable sets.