|A portion of the hill I ran|
There I said it. I hope that doesn't make some sort of weird masochist.
I think going downhill is a less controlled experience. Your foot sometimes slips a little, you're forever bracing yourself to prevent going too fast and toppling over, and the constant pounding of your feet all add up to a less than pleasing run.
Going uphill is fantastic though. I love just locking into a rhythm and powering my up the hill.
I recently did a 10km run over one of the big hills around my house and thoroughly enjoyed it despite the heavy rain. There was about a 200 meter gain.
I plan to do this run once a week. It really builds up the leg muscles and helps with stamina.