Using FPGA technology for event building tasks in high-energy physics experiments reduces costs and increases reliability of DAQ systems. In 2014, the COMPASS experiment at the Super Proton Synchrotron at CERN commissioned a novel, intelligent, FPGA-based DAQ in which event building is entirely performed by FPGA cards. The highly scalable system is designed to cope with an on-spill data rate of 1.5 GB/s and a sustained data rate of 500 MB/s. Its intelligent and highly reliable hardware event builder is able to handle and detect front-end errors and automatically take corrective action. In September 2017, it reached an uptime of 99.63%. The paper gives an overview of system details, performance, and running experience.