2. Performance
This is very nearly the most important aspect of them all. An incredible performance can make up for a bad venue, support act and even setlist. If the artist pours their heart and soul into the show and the audience senses it, they will react appropriately. Any good singer will not just sing but march around their stage with a certain finesse that only they could bring to the event. I could distinguish a show by The Killers from a show by Green Day simply by looking at silhouettes of the frontmeneven with the sound on mute. Brandon Flowers dorky dancing and Billie Joe Armstrongs manic hand clapping and shouting each bring an essential component to the atmosphere that makes their show uniquely theirs. A good musician who isnt singing wont try and take the lime light off of the frontman (or woman) but will engage with the music passionately and take cues to show off where necessary. They have their own unique moments to shine but most of their effort goes into a damn fine replication of the songs that got these people into the venue. Its still damn important, though, that they dont just stand there looking bored! Look at some YouTube clips of the artist youre considering buying tickets to. Do the things they say and do have a certain uniqueness? Do they have an original and distinguishable personality? You should feel that the song they are performing could only be performed in that way by that artist. And, of course, make sure they dont sound like shit. Its very, very important that the singer can singand the band can play. Auto-tune wont save you now Katy Perry.