Based on what I saw, I would have to say that Michael was poised to make a phenomenal comeback. He wasn't just planning a concert, but it was a massive stage production complete with 3D special effects, filmed sequences, and much more. He assembled an impressive line-up of dancers and musicians (my favorite being female guitarist Orianthi Panagaris, but the other lead guitarist, a male, ain't no slouch, either).
I guess what most people will wonder when they first go to see this is, how does he look? Well, he is very skinny, but other than that, he seems just fine. He's very courteous to his fellow performers and crew, makes his intentions clear without being a spoiled prima dona. Can he still dance? Oh yeah, he still has the moves, amazingly so. He never seems distant or detached, just his usual calm, reserved self that I remember from his 80's heyday.
The rehearsal footage assembled is pretty amazing. You see many songs performed close to how they would have been performed in the actual concert. The sound is very good, it doesn't have the feel of raw footage being shot by a handheld camera. The dancing is wonderful, and all the instrumentalists are great (and Michael isn't selfish, he allows them to be spotlighted). Also, they just seemed to be having a blast! This would have been one fun concert to be a part of. I don't think anyone was expecting this from Michael at age 50. He wasn't just going to phone in his performance, he was truly giving it his all, and it shows in the rehearsals.
You don't have to be a big MJ fan to enjoy this. I don't know how much fans were paying for the London concerts, but they were going to get their money's worth. Would Michael truly have ended his career after the London concerts? I don't know. After word got out how great they were, I think there would have been a huge demand for a worldwide tour. Based on what I saw in this documentary, I would loved to have seen the final, polished product (but what you see is still very impressive). This is only playing in theatres for two weeks, so go quickly, you won't be disappointed.