The trailer had me thinking that this would be one heck of a slice and dice fest in the same vein as Feast or even The Mist, with a group of rag tag survivors being huddled together in a diner / supermarket, and the fight for survival against invading monsters of all shapes, sizes and surprises. The latter film also had a bible-thumper, and religion forms the basis of the premise here, when you see how it all becomes a modern day reimagining of the tale of Mary, Joseph, and the prophetic messiah baby.
That's just my angle at making sense of the flimsy plot which didn't develop properly, despite ample time in the first half that had characters talking, rationalizing and reflecting on just what their predicament is, and how senseless it all seemed, at the expense of action sequences that undeniably got better as the film wore on. Amongst the action offered that I've not seen before involved the angel Gabriel (last done androgynously by Tilda Swinton in Constantine), which brings to mind just how angels would be clad for battle, with armour, close combat weapon with frills, and those metallic wings used both defensively and offensively in quite elegant ways as shield and blade combined in one sweeping motion. Not to forget, flight too.
Unfortunaately there are a number of close references to other films, most notably the Terminator movies and the Matrix combined for certain scenes that looked way too familiar. The beginning already had Terminator like arrival of the angel Michael (Paul Bettany) to our world, earmarked for destruction by God because he was losing faith in the bullshit of mankind. He's not following his book of Revelations though, as he sends his angellic force to earth mimicking how Terminator robots get sent back in time. Or the severe warping of the human face to indicate possession by a higher, in this case, spiritual force.
Basically, the world is God's matrix, and the angels being his agents sent to stop and destroy the birth of the prophetic Neo, who is but an unborn child in Charlie (Adrianne Palicki), an unwed mom who's waitressing at a diner out of nowhere aptly titled Paradise Falls, run by the estranged father and son team of Bob (Dennis Quaid) and Jeep Hanson (Lucas Black from The Fast and the Furious: Tokyo Drift), who get thrown into the thick of the action together with the rest of their diner crew and customers, which can be easily read as fodder for the apocalypse, which came in the form of a spider granny, ice cream man and the likes.
For the film to work, you have to buy into its reasoning that God has decided to end the world through an unfair battle using his angels against humans, and the absence of the Devil whom a friend thought would actually either rejoice, or would have gathered new followers with the exodus of human souls now being abandoned by the holy one. If you don't subscribe to this premise, then everything will not hold water, and it'll become just another mindless action flick that flits from one sequence to another.
And let me know if you don't agree that the baby is the messiah (if I wanted to go one step further it could even be the second coming), since every angel bowed their heads in reverence, and stopped dead in their tracks. It wasn't explained why the baby held the key to the salvation of mankind, so that's my speculation. After all, Michael the angel did find it worthwhile to switch sides in order to find some glimmer of hope amongst mankind to change his master's mind.
Legion had an interesting potential but ultimately got let down by its half-baked plot development and references so close you'd think it was The Matrix or The Terminator. It got played out too seriously for its good, though with room given for a sequel if one ever gets made given the way it ended (really like The Terminator again), and this time maybe with room to deal with the demons now that angels are likely out of the way.