Let's chill with the hyperbole until the movie has been reviewed.
Comparing any movie to "City of God" is a bit of an overenthusiastic stretch-you're talking about one of the best gangster flicks of all time here, and it was about as authentic as any movie of that particular genre I've ever seen.
Some of these Spanish flicks have a tendency to get mired in novela-type romanticism and sentimentality, a very obvious Achilles heel when a movie clamors for authenticity.
If the main focus of this film is a guy chasing a girl who was a long-lost love from the past as the trailer indicates, then the gangster stuff that transpires is just the backdrop to what could possibly be a very pedestrian love story.
Let's wait and see.