The special effects were absolutely gorgeous, and the 3D technology was placed to good effect here.
The technical details can really bog it down. I would give this a go if your a reader who likes psychological thrillers with hard technical details. Though apparently to some of the critics the science was dodgy in parts.
So you basically end up with a film that has questionable science, and sagged in the middle.
The character development however was rather decent.
In Short: Serve the needs of your story. Don't sag in the middle. But don't worry about being thriller paced either. The pacing kept the film from getting the four stars I would have otherwise given it.