The main differences are typical of modern music vs '60s music :
'60s - more swing, looser, more bass, more spontaneity, more subtlety and mystery, richer tone, serious approach, predominantly original.
modern - more precision, faster pace, tighter, more treble, more rigidity, perfect tuning and timing, sterile tone, flippant approach, predominantly imitative.
Unfortunately, many of these factors are beyond the control of modern artists. For a start, the recording equipment, setting and techniques are so radically changed now. Second, the artists themselves have been exposed to so much audio garbage for their entire lives. Third, music is now just one of many pervasive, easily accessed forms of entertainment. In the '60s, it was the number one focus for artistic expression for young people.