I just got back from this evening's performance, and I liked it a lot. I'm sure it helped that I splurged for an excellent discounted floor seat ($179), but it seemed to me like a solid play with a better-than-average Spacey performance.
Even though I had a good seat, I went up to the worst seats (that were being sold) to see how bad the view would be and, surprisingly to me, they didn't seem any worse than the back of the balcony at New York City Center. In addition, there were many more good seats than I was expecting. Also, I thought Spacey and his director made great use of the entire floor area and even the risers, allowing large parts of the audience to be much closer to certain segments of the show without (as far as I could tell) losing the other parts.
The main weaknesses, in my opinion, were: 1) somewhat bad acoustics -- although I heard every word without problem, the sound was overly echoey and the planes were a constant annoyance; 2) the last segment, about Leopold & Loeb, was set up in too perfunctory a manner -- the anti-capital punishment plea was neither as stirring nor as challenging as it might have been, because we learned so little about the child-murdering defendants and couldn't even look at flesh and blood human beings (just two empty chairs where they were supposedly sitting); and 3) this performance felt like what it arguably was, in effect -- a second preview -- and even though I thought Spacey's performance was first-rate, I could easily see it being even better with more rehearsal.
Overall, the audience seemed both enthusiastic and attentive. Perhaps it had something to do with the mix of subject-matter and sporting venue, but I can't think of any other theater performance that featured so many during-the-show cheers and ovations. Also, at the end of the evening, the standing ovation was immediate, enthusiastic and prolonged, and I happily joined it. Once it died down, Spacey invited a few dozen young students in the audience up onstage to take a group photo with him.