What do you like best?
Grunt's capabilities are phenomenal.
I've found Grunt makes managing resources for web apps very simple, and often processes that get very tedious can be broken down so simply; and Grunt can take over sorting through everything, while I focus on developing and writing code.
What do you dislike?
I find that some packages can be tricky with each other; sometimes causing issues because of dependency differences.
One issue I find most irritating is when I want Grunt to work in the background, and I don't want to have to check the status of the task if there's any issues.
It can be difficult if there's any syntax errors, and the package throwing the error is not detailed enough.
Recommendations to others considering the product
If you need a simple task runner, and you need something that's a little more configurable than Gulp; then Grunt is for you.
It has many packages, and can be used for a massive variety of simple tasks; for example, it can simplify a web app greatly, by bringing in file resources from all over the place, and placing them into one or two files (or more if necessary).
What business problems are you solving with the product? What benefits have you realized?
I do not want these files combined together.
I plan on using it to compile SVG spritesheets in the future, and I know it will be of great use.