I wish I could have gone to Metallica's S & M concert...
So far, I've been to three concerts.
The first one was a Gigantour; the bands were Job for a Cowboy, Children of Bodom, In Flames, and Megadeth. I'm not a big fan of the first three bands, but this concert was very appealing visually and audibly.
The second one was at Rose Quarter in Portland. That one had The Sword, Down, and Metallica. The opening bands were both fantastic, but James Hetfield had bronchitis during this tour. I didn't really notice during the concert, but the downloadable mp3s their site hosted afterward were terrible. This concert wasn't as visually appealing as the Gigantour, but the music was awesome at the time.
The third concert I've been to was here in Medford, in the Medford Armory. It had no seats, so my friends and I were standing for a total of six hours that night. I think the first band was Archer Nation or something; I don't really remember. The second band was Dope. I didn't pay too much attention to the music, but the mosh pits were pretty fun. After Dope was finished, Black Label Society took a fucking hour to set the stage. The music was awesome, but then Zakk Wylde went and had a twenty-minute solo. It was cool at first, but then it got tedious and boring.
Overall, I'd say the Gigantour had the highest awe-factor.