Let me be brief and to the point: if you are thinking of seeing this movie, don't. Save your money and your time. Really, I nearly walked out before it was over and historical epics are normally the type of thing I enjoy.
To expand: While some of the actors have some charisma, it is all buried in confusing, alternatingly hectic then boring scripting and editing. Great chunks of plot and meaning are removed to make way for histrionic and nonsensical dialogue (and monologue) we thought when the was of 1950s B movies (seriously, I and others in the audience laughed out loud at several "dramatic" moments particularly since for some unknown reason Oliver Stone decided to make all Macedonians echo Farrell's natural Irish accent, and direct Angelina Jolie to come up with the most ridiculous evil-Russo/Slav accent since Boris and Natasha). Characters come and go and yell at each other without us ever knowing their motivation or even who they are in the first place. No one is likable, even Alexander, despite Colin Farrell's attempts, because why they do what they do is left a mystery.
The most impressive and bracing scenes are probably the battles, but even they sometimes seem filmed as if from the point of view of someone who just stumbled into the middle of them and had no idea what was going on. Sure, there may be interesting points(ever see angry elephants facing a legion of pikemen?) and a good deal of gore, rushing about and and noble posturing. But more often than not, both within and without the battles, you will find yourself thinking "the who in the what, now?" as we skip inexplicably along to a completely different plot point, time period or area.
And what of the "gay" sub-plot? With all the smouldering glances and manly hugs, you get, again, about as much action as you did in a 1950s B movie - maybe less. Alexander seems not so much gay, straight or bisexual as just asexual. He does what is scripted, the filmmakers try to feel good about themselves, and we get nothing if not a step backward in the depiction of queers.
What's good about it? Well, they tried. I mean, you can see the millions of dollars stuffed into it. There are great masses of extras, impressive sets, a lot of pretty cinematography and one extremely beautiful horse (I would have rather watched Alexander's steed running about for a couple of hours, if I could). One of the baffling and sad things about it is, that they so clearly did try to make this a good movie. You can see the earnestness dripping off the screen, and particularly flowing from Colin Farrell as he tries to portray this historical giant among mean. But, ultimately, it is not nearly enough.
So, I say again, don't bother. The only other good thing about it is that it might make you curious to find out more about just who the holy hand grenade Alexander really was, and what really happened. I don't know about you, but I'll be trying to clear up that confusion elsewhere.