You can't force a group of classically-trained musicians to enjoy gaming music. They may enjoy it, I'm not saying they can't -- but they do or they don't; it can't be forced. It seemed like the orchestra at the re:play concert lacked commitment to their material. They were technically excellent, I think (from the depths of my musical ignorance,) but I didn't feel as if they enjoyed it, and ultimately I wasn't able to enjoy it either.
It reminds me of one of the long-ago Anime Expos. At that time, to fill the halftime of the masquerade, some high school students performed arrangements of Xenogears music. It wasn't brilliantly performed, but they were clearly doing it because they loved it, and that showed through. Hackneyed though it sounds, the performance had heart.
And there have been other concerts I've enjoyed. At Japan Expo, I saw a Lunar concert with IWADARE Yoshiyuki, and it was fantastic. I think, silly though it seems, that one could just tell that they enjoyed it.
But why do I have this opinion? I'm not a professional music critic, or even a person of normal musical ability. I struggled with this question a while, trying to figure out if it was just irrational resentment, and eventually I decided that the fault was with the music selection.
They were great pieces, make no mistake -- but they were also very popular pieces, and they were all energetic themes, and ultimately they just didn't mesh. There was no variation, no merihari. All main dishes, but no sides, no appetizer.
And because of the nature of their selections, they necessarily came from diverse games, which meant that we in the audience enjoyed entirely different tracks. I am a Shadow of the Colossus fan, while the guy next to me likes Bioshock. It was jarring -- I'd go from pieces I loved to pieces that I'd never heard, and without context, couldn't relate to.
I think they would have done better to discard the hero's journey frame and try for something less forced, something that allowed for more variety, more pacing. As it was, it felt like pandering, and I have been humored enough to recognize it.