If you are a medical student, researcher, or veterinarian looking for a powerful, free DICOM viewer on a Mac: Yes, Horos is an excellent choice. It offers 90% of the functionality of software costing thousands of dollars.
If you are a radiologist in a private practice needing FDA-approved diagnostic tools: Invest in Horos MD or OsiriX. The free version is not compliant for primary diagnosis.
If you are on Windows or Linux: Look into 3D Slicer, OHIF, or Weasis.