Covers shouldn't be pointless karaoke versions of the original (I'm looking at you Westlife) but the cover should become akin to the musical identity of the band covering it. For example, U2's version of Unchained Melody (on the B-side of All I Want Is You), Wheatus's version of A Little Respect, Gary Jules take on Mad World, and - most emphatically - Pet Shop Boys' magnificent cover of Always on My Mind (a number one smash here in the UK at the time, and still regularly tops all-time-greatest covers polls/lists). It is impossible to think of the latter as anything other than a Pet Shop Boys record. :)