running on motor oil wearing teflon boots?
You could get used of his inertia and correct the timing of you imput, if it follows some logic, but it seems that rules are complete random, and the most fantascientific thing is to sure-kill an opponent by a running jump, wich should be... maybe the word is... "somehow predictable" ?
Maybe u should integrate the bad physics in the plot of the game, by example, when the bad guys talk about how they will protect the area from trespassers... one of them may say: "And to be even more sure a trespasser get an hard time, we poured oil and fresh dead fish mixed with banana skin and bullshit all over the floor"
And then the hero may say: "that's too bad... and me being complete drunk won't help at all"
And maybe you should add an animation between the moment player releases the run button and the moment the charachter stops... but it would take maaaany cels, i guess.
Ok, there is no way to avoid the subject: unless he's running on a noticeably slippery surface his clumsiness in brake or invert direction doesn't make any sense.
If u "take your sweet time" the game is ridicously easy, but pleeeease, i bet it was, in your intention supposed to be such as donkey kong country.