In addition what the others have said:
LOVED:
the constant striving to do better, faster, neater, faster, better, faster, better, faster -- all while turning out a consistent product (not changing the menu every day still gives you a chance to compete against yourself!)
the constant learning -- about product, techniques, seasoning, etc. etc.
being given the chance to train others in the ways my chef wanted things, and then too in the ways I wanted them
being given the responsibility for creating parts of the menu, and for codifying them so that that's how they would always be
the adrenalin rush and being in the zone when the orders just kept coming (yeah, that's been said, but it's a drug I miss to this day)
HATED:
slackers who wouldn't clean and restock the station before leaving, so that I had to do that in addition to my own prep
unscrupulous owners who stiffed the staff (including the chef!) and their suppliers
the situation when other cooks on the line refused to coordinate getting orders into the window (only happened in one place, thank goodness)