The Mega Man X speedrun was fun, until I started hurting my hands on the bees at the opening. Never did Magic Carpet/Flying Saucer/Iceless route but the regular "slow" route was fun.
Got down to a 14 or so in SMW 11 exit, glitchless. That was fun until it wasn't.
And then there's Bonkers, with my two-minute-off-world-record-yet-still-in-2nd-place time. The execution on this one isn't as punishing and it's way more fun to go fast in this game than it is to play it normally. It's a Bad Regular Game but Good Speed Game.