I've seen it; very good film if not entirely original. I'd say it was like a cross between The Matrix and Eternal Sunshine, which isn't a bad thing at all, both are groundbreaking works.
DeCaprio was brilliant, to be honest I forgot that he was an actor and just accepted his character, whereas Marion Cotillard was just Marion Cotillard and I couldn't help being reminded of other films where she's given the exact same performance.
I like the way that there was no attempt to justify the existence of technology allowing people to share dreams. When you're making a film that explores an idea that isn't possible, I think it's better to avoid crappy movie science where someone in big glasses uses a stream of long words that don't actually make any sense. I think it's better to just say that the technology exists and leave it at that.
A suggestion for anyone who really liked Inception: try watching the anime film
Paprika. It's in some ways very different but it has a similar theme of diving into other people's dreams. Watching some of the dream sequences in it actually gave a a weird feeling of deja vu where it reminded me of my own dreams.