I like that they are very professional in their work, always taking care of all aspects involved with development tasks - from requirements to implementation process and even after launch.
The customer support department also helped us during several problems we had (including payment issues). They have an amazing team! We did our first project together about 3 years ago and since then there was not much change regarding quality of services provided by them. Their developers were able to solve any issue related with website's maintenance or new features' design/implementation.