Aside from one of the initial KenKen releases in the London Times (#18 I believe, which had a long outer border 44+ in ~14 cells), the next largest region I've ever seen in a KenKen is a 5 (one time) and then some 4's in some tough ones but mostly just 3 and 2 and 1. This may come from the fact the first 2 books were hand-written and then the rest were computer-generated with a not yet interesting puzzle generator that doesn't like taking things to a different level (or at least is scared of pentominoes).
I find a lot of the potential logical interest in KenKen would come from exploring larger shapes that interact with others in different ways. A commenter suggested no operations made a harder puzzle. Well, in this grid, there is one large operation but it is certainly not what's going on there in a now record 16 cell region.
This is a Wednesday, 6x6 Mediumer puzzle (if Easy and Hard aren't acceptable descriptions for KenKen elsewhere, then Medium isn't an acceptable description for me here).
Rules: Same as normal KenKen, fill one to six in each row/column so each digit is used exactly once. The numbers in the upper-left of each bolded region indicate the value for some operation (+,-,*,/) applied within each cell of that region but the identity of the operation is left as an exercise for the reader.