I've been following the Speedrunning community for some time now, despite the fact I've never actually tried to speed run a game, ever since I first saw that amazing video Quake Done Quick, way back in 1998? 1999? I can't recall the exact date, but I was simply gobsmacked by the way the runners had taken the game, which I had played for quite a while, and had dissected into its base components (the irony being, of course, when Quake done Quicker and Quake Done Quick With a Vengeance obliterated the previous run).
After that, I'd periodically check up on Speedrunning sites (above all Speed Demos Archive) and although it's rare, on occasion I still get that amazing sensation of utter awe, of seeing something I'd previously thought to be impossible, not only happening before my very eyes but usually followed by something other mind-blowing stunt. The classic examples are games like Contra III or Super Metroid (which I heartily recommend watching to anyone who's ever seen this game and that you can find at http://speeddemosarchive.com/SuperMetroid.html ), where the level of precision, skill and just plain awesomeness reaches ridiculous levels.
Even games that don't reach this level of amazing can still be a joy to watch, specially when you see tricks you've never seen before, or when the player manages to get the timing just right, or even when the sheer dumb luck (as in one famous Castlevania: Symphony of the Night run) that sometimes occur. It's a very satisfying experience.