I'm sure it would have been good. Besides that awful remake/retelling of Willy Wonka, Tim Burton usually does a great job and I'm sure he cast Nic for a reason. Everyone thought Keaton wouldn't be a good Batman and he turned out to be the best.
It would have been awesome, I am sure, and so fascinating in it's conception! The teaser trailer is so cool with Nic's bits of interviews and voice over! I certainly will watch the documentary when it comes out. I am not much into super hero movies, although I watch them with my dh, but Superman has always been my favourite, I used to read the comics when I was a kid, and I think the Christopher Reeve was wonderful in the role, I love those movies. Nic as Superman, though, wow, that concept just blows my mind!
Tom Burton just knows what he is doing. It wouldn't have been the most, for want of a better word, 'classic' Super-Man butrim sure it would have been great! Saying that, people are quick to forget, that the Batman of his was hardly zany or anything, it was quite good.