Ease of use, high performance, low footprint, great support, ability to scale, excellent documentation. The lack of features for some data types (numeric, date times) can be a problem. Highly recommended! We needed a system that could handle our transaction volume without being a resource hog. We were also looking for a good way to expose business metadata via REST-based APIs.
Data integrity was very important to us as well. I am pleased to see how quickly we've been able to get up and running