Punch Club is about training, improving stats, getting new abilities, and then using all that against other opponents in a fighting league. It kinda has a Rocky vibe to it. That underground old school boxing training. Kinda.
But really, at it's heart, Punch Club is an optimization engine. It's for people who love to optimize everything. If you're a theorycrafter or optimizer I can't think of a better game for you.
While I like RPGs that allow me to find efficient ways to do things... there really isn't much more here. It's just an optimization engine. That's not enough to hook me. It doesn't help that the setting and themes are ones that particularly appeal to me.
But if you're someone who loves to optimize the hell out of your RPGs, you really should take a look at Punch Club.