I actually do find his "child in a grown-up body" schtick to be hilarious, because he puts all of the child into it. Jerry Lewis, et.al. put the cute waif into their act, but Atkinson throws in the absolute bastard that also lurks in children. It's the wantonly cruel aspect that raises him above the others to me.
Well, that and the Rube Goldberg ideas he comes up with to solve his problems, like painting his apartment in a flash.
But then comedy is a very personal thing; if it was up to me, David Spade, for example, would be in Gitmo...