My opinion: overblown nonsense that was slightly relieved by some clever CGI. But puhlease, any dream within dream story is just a license to be silly (see Dallas circa 1985). It was sub-Matrix with a large dose of Cubby Broccoli. And as to the fantasy city Cob & Mal built over 50 years, Christ, they were architects and managed to come up with the most banal cityscape possible.
I'll confess that there was some good acting and that the combination of Leo Di C, Ellen Page and Joseph Gordon-Levitt worked well.