Sue, I'm not a singer, but as a listener I've often found that an understated performance that allows the audience to concentrate on the song, not the singer, works better for me. On the other hand, 'not too much emotion' may give the wrong idea. The singer has to be able to convey his emotions about the song, just not tip over into sentimentality, or appear to give presentation, vocal artistry or whatever pride of place above the song itself. Hope I've made myself clear...!