Focus is a film; that ironically, has no focus.
Focus is a 'dark romantic comedy' heist film, that can't quite decide what it wants to be. Does it want to be a heist film? Does it want to be a romcom? And because it meanders between the two, it never really succeeds at either. And in all honesty, it's a horribly bland film that's a waste of time and money. And in this case, I'm referring to my time and money.
So the story is about this professional conman; Will Smith, who's cynical etc etc. Imagine the stereotypical cynical person who refuses to let anyone close to him for fear of being hurt. Then there's Margot Robbie who's some newbie that he takes under his wing. They go through some scams in New Orleans and they hook up and then he dumps her suddenly; because y'know, he's afraid of being hurt and all. And suddenly half the film is over by that time, just building up the backstory for two characters when they could have just introduced them and hinted at the backstory. Then the later half occurs 2 years later when they meet again when Will Smith is hired to be on another con and Margot is 'dating' the person he's working for. Then insert some heist-like moments and a standard twist ending and boom, you've got Focus.
I'll address the two very different aspects of the film seperately. As a romcom, it fails horribly. I didn't really feel that Will and Margot had any chemistry on the screen and honestly, whoever wrote the romance aspect of it seriously doesn't seem to understand relationships. So...the two characters meet and then they fall in love. Just like that. No spark, no chemistry, no nothing. I almost thought Margot was trying to set up Will as part of a longer con because that's how fake I felt their relationship was. And to be honest, that might have made for a better film.
As for the heist aspect of the film... Have you ever seen a heist film that really only has TWO characters in it? Because I haven't. And that's part of the issue here, the really really weak (and non-existent) supporting cast. There's no zany wackiness like there is in general heist films. Instead, the first 1/2 of the film is spent on doing boring cons like pickpocketing and gambling etc. The second half involves Will Smith doing stuff by himself while trying to get back with Margot. Neither half is particularly interesting.
Overall, this was a pretty blah film. They could have skipped the first half of the film; where they show the start of the relationship and just skipped to the heist in the second half, as well as adding more people to the cast. Introduce Margot as a disgruntled ex or something. Add flashbacks or retelling to talk about the romance. Or at least come up with a better romance.