The digestive system really is crappy. I doubt it even changed much from our farther ancestors. You even have to get bacteria in there to do its job.
But I don't understand the complaints about the nervous system. Sure, it has its hiccups, but overall it's the most advanced human subsystem with its vast capability to process and store information. Of all the organ systems, it seems to be the only one that grants the capability to go into space instead of hindering it.
Surprised there are no complaints about hormones and immunity yet.