Both lack sufficiently high stakes, for starters. Mr and Mrs Smith is about two professional assassins who go on the run when they fail to kill each other and their bosses put out a hit on them. And we are supposed to care about them... why exactly? Not only do I not care about their fate, it's an inevitable done deal that they will survive, because they are super, highly-trained killers. So they can't die, and I don't really give a crap either way.
Plus, the bosses are faceless shooters. We never get to properly see the people the Smiths are up against - just endless black-clad bad guys. And you really miss a well fleshed-out villain like Hans Gruber. Big time.
In the Adjustment Bureau, Matt Damon and Emily Blunt are at least a likeable lead couple. Early on, Matt is kidnapped by the Bureau men and threatened with getting his brain fried if he continues to pursue his girl. Great - now we have people we care about and high stakes to go with them. Except that the rest of the movie proceeds to totally water down the threat. Matt keeps getting caught by the Bureau, and at no point do they follow through on the brain-frying, or even look like they're about to.
The result? Toothless bad guys and as a result, no real fear factor. The stakes dissipate, I start snoring.
The moral of the story is, raise the stakes as far as they will go and when you have a bad guy, make him bad, but with a personality! Hans Gruber from Die Hard quotes Alexander the Great AND shoots Holly Gennaro's boss in the head within his first five minutes on screen. We can see that he's ruthless and totally evil, and there's still a whole movie to go!
What about YOUR villain? Can he compare with Hans, or is he all talk and no action?