Mad World is a Tears for Fears song. Nothing Compares 2 U is a Prince song. Hallelujah is a Leonard Cohen song. Hell, Jeff Buckley's cover is basically a cover of a cover since it's based on the Jeff Cole version. While credit should always go to the original artists, I'd say the cover versions of ALL of these songs are sadder than the original, and in many cases are more epic, dynamic, whatever you want to call it. There's a reason why the cover versions are much more remembered. Hell, when Trent Reznor heard Johnny Cash's cover, he realized it wasn't his song anymore.