What people often miss with J is how good it is for exploratory programming due to its terseness and most importantly its integrated columnar store. It replaced R for data wrangling in my stats programs, and relegated it to just running the models.

Once you get used to it, it's really a breeze and far easier to modify than 500+ sloc R scripts.

Of course, that does not work for everyone, and especially not for big teams, but still!