I actually just downloaded and saw TRON for the first time about a week ago.
TRON came out in 1982, which was a golden year of sci-fi in movies and it is really quite good. It just works.
I watched it and while I enjoyed it, I was impressed at just how immersive the whole thing was. It still feels unique and interesting. It doesn't feel like a pale foreshadowing of THE MATRIX, for example. It holds up and is entertaining. But what made me realise just how much I actually enjoyed it was that I was watching all the TRON LEGACY trailers online and was really, really excited. It kinda snuck up on me how much I evidently enjoyed it. It's just solid entertainment and I'd suggest watching it before the movie. Just download it. It's short, sweet, entertaining, and while I'm sure the new movie will be understandable, it might suck and if you enjoy TRON that might carry over and help you enjoy the new one.