It was my first time seeing Opeth, but I thought they were amazing. Nearly flawless, at least where it counted.
My biggest complaint was Tapping the Vein. They had a decent sound, but I was quite unimpressed with the way their singer conducted herself. At one point, someone from the crowd yelled, "play some slayer!" and she got all pissed off, calling them an ass and generally whining about how they had it rough being an opening band, etc etc... I found it quite boorish and unprofessional. The crowd already wasn't on her wave, so instead of trying to win us over, she attacked. It was quite embarassing. I was embarassed FOR her. I don't think TtV won many fans that night.
But Opeth made up for it in spades.