I practically live and die by the 5 Minute Rule, and as a counterpoint, I've always found Grunt intuitive, if verbose. In particular, I love that its files API is so flexible. I frequently find myself asking questions that look like "I wonder if I can do this X way", and things just work.
Saying Grunt is "very bad" is harsh and only serves to amplify hyperbole that causes much of the churn around JS tooling.
[edited for a grammar nitpick]