Ease of use and amazing customer support are by far their best selling features. As a developer it's invaluable to have someone right away to help you with your problem, saving a lot of time and patience. As an end user, the navigating and use experience is really important on determining the level of trust in the data and the tool, and second, the likelyhood that they're going to continue trying to get insights from data. The platform used is very important and Looker achieves that successfully!
There isn't much I dislike, but some very minor inconveniences such as browsing between the documentation platform and the forums.
Looker has helped us get rid of the data breadline and give data to the users when they want and how they want it without relying on someone to hand it to them. It's also allowed us to spread data and data usage to more than just a handful of users, spreading it at company level so everyone can get insights out of their data.