Personally liked the goofiness of GM mode in NHL04 the best.
You win multiple back-to-back Stanley Cups, and each great accomplishment you make is followed with unlocking decorations and new colors for your office as if that was your goal all along instead of the usual Hockey accolades.
No other EA game can match the sheer fun of winning the Stanley Cup with your in-game franchise and then unlocking a lava lamp for your desk as a reward, how ridiculous it all is that the requirement to put a freaking lava lamp on your desk can be nothing less than a Stanley Cup win.
And I liked messing around with the GM office, make it as ugly as I could (which wsan't hard with how many ugly decor items the game generously gave), and then watch as my GM character would lift his face off his desk, look around him a bit, and then nod in satisfaction at the "marvel" I'd put together each time I made a ridiculous change to the office.
Plus, NHL04's trades are deliciously ridiculous. I enjoyed taking the litteral worst players I could find there, and then through multiple trades transform them into superstars of the time like Lemieux, Sakic, and others in less than a day.
Ah, good times, good times.