What do you like best?
I like how they've tried to make the Github issues look a little better and they've helped make kanban a little more manageable with all their awesome reporting.
What do you dislike?
In trying to make the issue creation look better, it's left off some of the functionality you can do right out the gate with Github, like dependancies, but you can add it in after the issue is created.
Recommendations to others considering the product
Zenhub is really useful in their boards and reporting, to me, the reporting is enough in itself. As said earlier, for reporting to work, you must stay convicted in your process
What business problems are you solving with the product? What benefits have you realized?
Their reporting has helped tremendously with estimating our projects for clients. Anyone in web development knows this is the most difficult thing to do, but by creating an issue, allowing to evolve over time, and making sure to fill in all the information like estimate, release, and milestones; the reports will show you what you lack in your estimating over time. You will progressively get better with this, especially if you stayed convicted in following the Agile Web Development process.