What do you like best?
It was a nice attempt to update the User Interface and begin to consolidate a look and feel across the product line of desktop, laptop, tablet and phone. The boxes were colorful, the memory management was improved and it was built with SecureBoot, which was a great step in security. The initial sign-in screen was beautiful with the artistic Seattle skyline.
What do you dislike?
It was rushed. There were very few positive reviews of this from early adopters, as well as technical and non-technical writers and bloggers. The login screen was beautiful, but not very intuitive. Once you signed in (with a required Microsoft account, which was another bad idea), nobody knew what to do. Or how to get your desktop. Or log off. The Charms bar was hard to access, the look and feel of Windows that they'd build since Chicago was gone. People were lost, and people lost interest.
Recommendations to others considering the product
Personally, I would recommend going to Windows 10, as they've seemed to fix the User Interface to have that Windows look and feel they've had since Windows 95 with the up-to-date cross-platform interface they have with the Windows phone UI. I know some places aren't comfortable yet with Windows 10, so I'd recommend Windows 8.1 as it took a lot of the pain points of Windows 8 and improved on them.
What business problems are you solving with the product? What benefits have you realized?
None, and none. Outside of our QA and Surface RT users, we never adopted Windows 8, or Windows 8.1. We waited for Windows 10.