Direct Metal Laser Sintering has emerged as a key additive manufacturing technique for producing titanium-based biomedical implants with complex geometries and tailored porous architectures. Despite these advantages, as-built DMLS titanium surfaces exhibit limited bioactivity and insufficient antibacterial properties, which may compromise long-term clinical performance. This review provides a comprehensive and multiscale analysis of surface engineering strategies aimed at enhancing the biological performance of DMLS titanium implants. Mechanical treatments, chemical modifications, bioactive coatings, and antibacterial functionalization approaches are critically evaluated with respect to their mechanisms and biological outcomes. Particular emphasis is placed on the interplay between surface topography, chemistry, and wettability in regulating protein adsorption, cell behavior, and bacterial adhesion. The analysis highlights a fundamental trade-off between promoting osseointegration and preventing bacterial colonization, which remains a central challenge in implant design. Comparative assessment of existing methods indicates that no single modification strategy fully satisfies clinical requirements. Instead, multifunctional and hybrid surface approaches that integrate bioactive and antibacterial features demonstrate the greatest potential. Key challenges, including process variability, coating stability, scalability, and limited clinical validation, are also discussed. Future directions focus on the development of bioinstructive and stimuli-responsive surfaces, as well as the integration of data-driven optimization methods. Overall, advancing DMLS implant performance requires coordinated multiscale surface engineering combined with clinically relevant validation strategies.