Alex Cross is a story of a detective and a serial killer, with lots of Bullshit thrown in between.
Now that's a pretty succinct summary of the film but just to be clear, let me go a bit further in-depth into whatever passes for the plot of the film. It's about a detective; Alex Cross, who's basically a modern day Sherlock Holmes/Poirot and how he's on a team with his childhood friend; who's secretly banging the only female member of the team. Eventually, they cross paths with an assassin who's been killing people in their jurisdiction. This leads to a lot of gratuitous torture and violence and a lot of bad acting and bad dialogue, eventually culminating in the 'twist' ending which involves the detectives setting up the main villain as a fall guy for another charge because they can't convict him of the first charge; that of multiple homicide.
So what's wrong with it? Lots. The plot is just ridiculous at times. The sheer number of deus ex machinas is mind-baffling. For example, in the last part of the film, Alex Cross and his partner are racing in a car to get to where the assassin is; having tracked his location via the GPS of his car. The assassin in the meanwhile is driving out of a multi-storey carpark when suddenly his car is rammed by the detectives car. You think this is the first intelligent move the cops have made so far; disabling the guy before he can retaliate but you'd be wrong. Apparently it was all an accident. They didn't even aim for him on purpose. How could they? They didn't know he was the one coming out. Which meant that they would have hit ANYONE who was coming out at that time. Seriously, wth cops? It's not even like they were going at a very slow speed either, you can see the assassins car literally go skidding away from them. Yeah, what if that had been a civilian?
And somehow, the assassin can just walk away from the damn accident almost instantenously. This is despite the fact that the drivers seat in his car is on the left; it being a US film after all, and the fact that the cops rammed him on the left side. The man should be dead after that impact. Dead or severely injured. Not running off to have a final climatic fight scene with Alex Cross. And that was just one of many WTF moments.
And then there's the bad acting. Some lines were just so painful to watch because the actors clearly weren't giving it their all. Especially the last scene, where the villain starts speaking in his horribly fake french accent 'noooo, you can't do this to me'. It just felt grating to the ears.
Plus there was just one more thing I felt I had to add. In most american action films, the women are there just to be eye-candy. Helpless and waiting to be rescued while ultimately contributing nothing to the plot. Alex Cross doesn't quite follow that stereotype. Instead, in it, women are there to be helpless, then tortured and then killed. Seriously, when you have 2 of the main women/girlfriends of the cops get killed by the assassin without any other sign of a female lead, you have to wonder what kind of signal the writer is trying to send across.