Precisely, the depth of a good fighter would be so deep i think it would take forever like you said. So i'd always have something to learn unlike RPG's wich believe it or not actually have less depth, though i do love them also XD.
For me, it's so deep and uninteresting that I'd play it for a little while, and maybe pick it up and play once and awhile, but I'd never have the ambition to master it. The content is there, but my interest isn't.
Earthbound! It's a true classic as far as I'm concerned, even though it's probably considered overrated nowadays. It was also the game that introduced me to RPGs. I'll never forget how awesome it was to explore a huge open world for once, and all that quirkiness that made Earthbound awesome. Giygas still creeps me out a little, even today.