[gcanyon]

Experts in J say something like, "If you think through the problem, you've solved the problem in J"

I definitely agree that "can outsiders, or even less experienced coders, understand it?" is orthogonal to "expressiveness." I went a little harder than I intended listing that as a drawback to expressiveness, although it's certainly a complementary feature: given two languages of equal expressiveness, the one that encapsulates that range in more comprehensible terms is "better" (there are many other factors to consider, hence the mitigation quotes).

I love the fact that in J:

    mean =: +/%#

Meaning that you can express, from primitives, calculating the mean average with just four characters. And even with my very weak J, that's clear. But then I look at something I wrote over ten years ago:

    candidates =:,/((_4]\4#"3 (_1 + 2 * #:i.2^9) (* &. |:)" 1 _ list)  * (>rowSigns))

and I have zero clue how to interpret that. It's almost certainly not idiomatic J, so it's possible (likely) that it looks like garbage to a J expert as well. Certainly J's terseness doesn't lend itself to commentation. :-)