I'm a big fan of the 16th and 17th century German chorales. They seem to be very singable by the average person, and can be done beautifully by a congregation a capella, even though many of them were harmonized by J.S. Bach and meant to be played on the pipe organ. That said, I come from a church tradition steeped in four part a capella congregational singing. So we sing them well.

Singing four part harmony is for me a metaphor for life on Earth; all the people blending different voices, and different vocal lines to create real harmony. Sometimes, as in Lowell Mason's setting of The Doxology vocal lines act independently, yet give a sense of purpose, strength, and a common goal.

Singing in unison (eenstemme) is a metaphore for everybody doing the same ol' thing the same ol' way as everybody else, and done badly is just uninteresting. Praise music that I have heard qualifies for this category. Taize, on the other hand can be and is in our church sung in four part harmony, sometime a capella, sometimes with instrumental accompaniment.
Jim