I believe critical hits make combat fun, brutal, epic even, and give little guys the possibility to beat a stronger/ bigger enemy., and that's the way I think it should be. Anything can happen and any model can turn things around.
Remember Mordheim Critical Hit Charts? It made for fun memorable gaming moments, the kind of moments your remember for years!
I'm more concerned with the initiative roll, that's where randomness should be curbed. Warbands should start the round with the same number of ability points, like you get 6 ability points each round to use as you want. Unused points cannot be carried over to the next round, but leaders could generate one extra ability point per round that would carry over. I'd make it easier to plan ahead some spectacular actions and no player would get an edge over the other because he rolled a quadruple and his opponent only a double. That would definitely make the game more competitive I think.
My 2 cents !