Its the command systems, both DCS and Legacy, that continue, after decades to challenge me. I think I am one of those guys who prefers "to get things moving along" rather than figuring out the nuances of the systems. I loathe staring at remote screens programming features...and then having do it again because of some technical glitch.
If you really want a challenge install a couple of 45 degree crossings and run a couple of trains at once (assuming you're in command mode).