Simply one of the best interview experiences I have had. Everyone was very professional and positive, the HR asked reasonable and mindful questions - not just 'tell about yourself'. Be ready for some simple technical questions on this stage. The technical interview was great, too - with clean explanation about how the work is done in the company, and pretty interesting code review task. Stas, the interviewer, navigated the flow of the interview very well and professional.
As the actual product is multithreading-heavy, it is very important to have appropriate skills and experience in Java. If you have not been exposed to multithreaded environment in your experience, it may be harder to nail the tech interview and the test task.