Soju is absolutely horrendous, and gives the worst hangovers I've experienced even without drinking to excess. The most palatable soju I've had was the Hallasan soju from Jeju, which was smooth and similar to a midrange shouchuu, lacking most of the awful aftertaste that ultra cheap stuff has from all the formaldehyde or whatever embalming fluids they use. I've had bad sake and bad shouchuu, but even good soju doesn't much appeal to me.
interesting fact, jinro soju is the #1 highest selling liquor in the world, at something like 63 million crates for the year. Smirnoff Vodka is #2 at 1/2 or 1/3rd that much, and #3 is Lotte brand soju. And something like 97% of all soju sold in the world is sold in Korea.