Yes, it's flawed - especially if you're into Hollywood films that demand a lot of effects, a purely entertaining or fantasy story or plot, and you can't actually think for yourself.
Roeg's films are for the intelligent film-goer, and Insignificance is a perfect example.
The characterizations are brilliant, the story is excellent, but, like all Nic Roeg's films - it has you thinking on every level about aspects of reality that would never have dawned on you before. His films always make you think, and personally, I like that in a film.
So don't expect to come away from watching this film and feeling all happy-happy, because it's likely you'll be disappointed.
But I think it's excellent.