Game series you like but still have not played part of the series?

[Raven]

Zelda, but haven't played the GBA or DS titles.
Metroid, I haven't played any outside of Fusion
Castlevania, only played IV, Circle of the Moon, & Dawn of Sorrow.
Halo, only played 1 & 2

There's definitely more but that's all I can think of off the top of my head.