Review in a Hurry: You can't just play mad libs with the terms "James Cameron," "underwater," and "3-D," and expect automatic Titanic. There kinda has to be a good story and passable acting involved, and this is where Sanctum (actually directed by Alister Grierson) sucks it.
The Bigger Picture: The inherent claustrophobia of caves can make for instant cinematic tension. Doesn't matter whether the other elements of the movie are good (The Descent) or mediocre (The Cave). If you throw your actors into a tight space between rocks, you guarantee automatic panic attacks from a certain percentage of your audience.
One would think doing it in 3-D would be even better for making pulses race, but it doesn't seem to matter that much. Close-ups of limbs trapped in rocks can only be filmed so many ways, after all (and 127 Hours already exhausted all of them). There isn't as much of an opportunity to throw stuff in people's faces while that's happening.
Or maybe it's merely that Grierson isn't an especially good director. The preponderance of evidence suggests it, as a matter of fact. He gives us a group of people going into an unexplored series of caves, many of which are underwater, and we can tell these folks apart primarily by the fact that one of them's Ioan Gruffudd (with fake American accent shakier than ever), one's a kid, and the rest aren't.
Lo and behold, the cave caves in, water and rocks blockade the way out, and the only escape is to find a new, undiscovered passage. In the "true events" this movie was loosely based on, everybody came up alive. Here, a body count starts mounting. And the one advantage of having such a generic, mostly no-name cast is that you genuinely can't predict who will die, and when.
The 3-D, shot on the Cameron/Pace system, is fine, but doesn't add a lot. It's just a shame we don't have the technology to post-convert the two-dimensional performances.
The 180--a Second Opinion: The one actor who does deserve some credit is Richard Roxburgh, playing the hard-edged veteran of the group. If you didn't already know it was him, you'd never recognize the villain of Moulin Rouge, or Van Helsing's Count Dracula.