The mezzanine at the Harvey has a reputation for being especially bad, but for my money I never thought it was as bad as everyone said. I always like to sit in the far left or far right in the front row of the mezzanine. Good bang for your buck IMO, but some feel it's too steep and high up. Legroom isn't great, but I can manage and I'm 5'10". I prefer it to the rear orchestra, where you can get swallowed up in the overhang and the pillars. Obviously if you CAN get the front section of the orchestra, that's the best.
I saw this show in London - I thought it was really smart, but didn't totally land for me. I like my Cyrano retellings with a little more warmth. The pacing was a little weird for me too, but I also found it a little bit difficult to fully engage with it since I had an obstructed view. I felt pretty detached from the whole thing, and it's like 3 hours long.
Still recommend it to people though. It's a cool take on Cyrano, and McAvoy is great.