Saw this yesterday with a friend of mine, and while it was great to be able to go, the sound really let it down. It was incredibly loud and often distorted during the slower songs. Tinny and thin is how I would describe it. I had to put my fingers in my ears to dull the shrill treble!
The avatars are mostly good, but occasionally the mouth movements don't keep up with the vocals, and there are occasional lapses in facial movement to remind you they're not real.
We were disappointed that Eagle (along with a couple of other tracks) was accompanied by a lengthy anime type cartoon, instead of the avatars performing. Also, although most of the time the avatars were projected onto massive screens, there were times when they weren't, and you struggled to see them on stage.
The live band was very good and the special effects were fantastic. However, we felt sorry for the those on the dance floor, as there were so many slow songs they didn't have a lot of opportunity to dance.
The show was still an enjoyable experience, but for the price of the tickets, we expected flawless sound, and it really was not. Take earplugs to tame the overwhelmingly loud and shrill treble! Glad we saw it but wouldn't see it again unless they fixed the sound, which was seriously poor quality.
Finally, if you don't want to walk from Stratford to the arena (about 25 mins), get the DLR from Stratford (platforms 4a and 4b) to Pudding Mill Lane. It's one stop and a few minutes, and right opposite the park.