Erm, I mean you should always focus on quality over quantity. I mean I don't think having a little more levels is bad, nor do I think having a short game is bad.
I guess if I had to pick, I would say just do what Buckshot Roulette did and focus on a nice short experience and having an endless mode. (Although I doubt people would really bother with a few levels)
EDIT: Also i'm not sure what kind of story you're making, but maybe this video could be helpful:
it's made my Masahiro Sakurai (yes the guy who made Kirby and smash bros.)