So... Jacko's rehearsal footage of what would've been his final gigs has been stuck together by the bloke who directed High School Musical (Kenny Ortega) and is now on the big screen within months of the legend's death. Not a good sign.

Here's what you need to know:

1. The pic's opening dedication 'For the fans' is a bad start. Directors say their film is 'for the fans' when they know that the majority of ordinary punters are gonna hate it. The movie proper then begins with dancers in tears telling us how happy they are to be working with MJ, then some Wanna Be Startin' Somethin' trial runs. To be honest, it's average.

2. But the music sounds amazing. Michael's vocals are patchy - he wasn't even trying to be 100% - but the band is tight, the editing tighter, and played over cinema speakers the classics send shivers down the spine. But still Jacko seems like a shadowy figure. Designers, choreographers, costumiers are all interviewed but MJ is a mumbly man in the background for the first 20 minutes.

3. Then we start to really see him. The perfectionism, the easy going chats, the gags. Whilst this is definitely not a film about Michael's private life, we see a clear picture of a professional. Every aspect of the impending show is in his head. He knows exactly how he wants it to be and is happy - often hilariously - to tell everyone. He looks at home on the stage and his ambition knows no bounds. Yet he's also very casual and it's certainly the most I've seen of Jacko as 'just a guy', the kind of man that his friends have been saying he is for years but which the media liked to ignore.

4. So the movie becomes a snapshot of what could have been. A performer who appears to be on top form smashes his way through umpteen tracks and has a vision for a spectacular event. We can only sit back, enjoy at least having this much, but also muse on what could have been. It's pretty electrifying, actually.

5. And what you're left with is a breathtaking but undeniably strange viewing experience. This is a movie that only got made because its star died. It's been hyped beyond belief yet details have been kept meticulously secret. Just watching it at the London premiere was a major event (for starters, it was at 1am!). Normally that kind of buzz shouldn't affect a film review but then this is no ordinary bit of pop culture. Its peak into a theatrical world is in itself fascinating, a great little film on preparing for a show. But tap yourself into the fact that you're also witnessing a bit of showbiz history and This Is It becomes an incomparably exciting film to watch.