What do you like best?
I love the direction Apple is headed with its Cloud services. It's a comfortable feeling for the user to have multiple devices in sync without having to take the time to to so manually. I also do a lot of troubleshooting that involves several windows, and the multi-desktop option is great for that.
What do you dislike?
Working in Networking, a lot of software is made for Windows only, which is a hassle. Fortunately, though, Bootcamp is a thing. Capitan also introduced (I think - maybe it was Yosemite) a new Rootless Protection default that I had to disable in order to have my USB to Serial adapter recognized. While I recognize that was a precaution primarily for the average user, it was definitely something I struggled with for a while when the issue first arose.
Recommendations to others considering the product
For current Mac OSX users, the upgrade is no question. It's free, it's good, and it's pretty. If you don't have it/a Mac in general, learning the new OS can seem daunting at first. But the way the user interface is designed in combination with the multitouch trackpad and other optional features Apple provides, the working process becomes more fluid and second nature with time. It's truly a great product, and I'd suggest anyone considering it to give it a try.
What business problems are you solving with the product? What benefits have you realized?
Most of my work revolves around troubleshooting end devices and networking equipment to provide and verify network connectivity on a very large campus. My fluency with Mac OSX has helped me do my job more quickly and efficiently in a way that wouldn't be possible (for me) with other operating systems.