Final Fantasy III. I've been on an RPG kick lately, and thanks to ZombiePie's continued exploration of the series, I'm determined to finish most of the single-player Final Fantasy games, too. Prior to this year, I'd only completed Final Fantasy I, II, and XIII, though I've always been interested in other installments.
I know ZombiePie said he feared Final Fantasy III at the start of his Final Fantasy XI blog, but for anyone with the same hesitations, it's entirely doable as long as you're not averse to grinding or using a guide to plan out your job composition. That said, I'm also playing on an emulator, because the speed-up button trivializes the fear of leveling the wrong class or acquiring money.
If I had more time or didn't have 15 other entries I've yet to play, then I would commit to seeing Final Fantasy III through on official hardware (it's currently installed on a Vita slowly gathering dust). As an adult with bills and a family, however, that's a luxury I'm simply not afforded.