Legion, with a plot that seemed patched together from Demon Knight, Terminator, and The Prophecy, in short, holds a lot of promise.
It has many moments of goodness, but they are stretched out far too thin, and in between are some moments that feel like an attempt to add dimension to the characters so that critics won't complain that it is just wall to wall action. Character development is good, and any one of these scenes on its own would be fine. An audience can't be expected to sit patiently for the entire middle portion of the film while everyone airs out their backstories and "meaningful" character flaws.
The director was most likely worried he would be accused of "showing off" had the film been a non-stop effects showcase. And since a trilogy is in the works, it wouldn't be wise to deny the fact if he was trying to get as much story out of the way now so that he could focus more on action in the next two films. However, the effects are grand, and thus more is wanted of them, and it's doubtful that the film will connect with enough audiences to get those followups.
But, there is a lot of potential. Paul Bettany is a great action hero, and it's hinted that his character, Michael, may not be as pure and good as the others would hope. Likewise, Gabriel (played by Kevin Durand) is his equal, and despite being the film's de facto main villain, he doesn't seem to be out for the count yet. And they barely even scratch the surface in regards to the baby that the whole movie centers around. Legion never really explains what Charlie's (played by Adrianne Palicki) child is supposed to accomplish, and why she was chosen to carry it, for that matter. Most trilogy openers work as a standalone film, but this one is maddeningly left open for followups.
The movie does a fine job of putting all the characters on equal terms, so that you're not sure which ones will die, who will turn, and who will save the day. One character's death in particular was shocking; it's someone that always seems to survive a film, and they are dispatched long before the conclusion as well.
But, the cast makes the abundance of generic character development even more complex. Most of the actors don't need a backstory to latch onto. Ironically, the character that gets the least amount of characterization is Charlie, who audiences are least likely to be familiar with, and yet is the most important character.
It succeeds on a technical level. The effects are outstanding, and the action scenes are easy to follow and largely epic. There's a great sequence where Bettany and the others have to keep a parade of cars from getting to the diner, and it's both exciting and somewhat unique. There seems to be some missing scenes here and there, but it's otherwise well edited, and the surround mix is terrific. The only legitimate problem is the bizarrely stunted pace and far too dependent-on-sequels approach.
A sequel will come to pass and maybe deliver on the promise of the concept. It would give studios and filmmakers some pause before green-lighting another film that's designed to only tell 1/3 of a story. To conclude, fans are still able to enjoy a more or less complete tale.