The decors and set pieces, aswell as the costumes, of Leone's westerns were fairly realistic I believe, especially to these mid 1960s films compared to the previous Hollywood versions.
I'm no expert of the western era, but other people have made such remarks, Christopher Frayling for example.
Other than that Leone's intentions were to make an anti-western or a rock n' roll-western, to deliberately break the traditions of old fashioned western movies.
And also generally have a very nihilistic and sardonic outlook on most things (which you can relate to even in your own life )
His later films can however seem overlong, too slow, too big, and in the case of OUATITW even a little pretentious.... forgive me :o
Maybe this can give a lifeless impression?