I thought maybe I was too lenient on live bands for a while, because I kept seeing bands that I didn't really care for that just put on a great show (because they were with other bands that I DID like), but then the last show I went to I almost left fucking mad because the support acts were absolutely fucking terrible (Glassing and some local garbage). But yeah, I put on a Blood Incantation song the other day and it was just lame. Great live though, if you've got another reason to go.
All Them Witches is another one. Can't fucking stand any of their albums. Saw them live (they were playing with King Buffalo), and was like "What the fuck is this band?!? They are great!!" Double checked by trying an album again, and, nope, they still sucked. And that was at a clean show, so can't even blame the contact high or anything.
Hate to support the cliché, but some bands are just good live and only live.