Finally caught up with this after being tempted back to it by your review and I must admit, it's a far better film than I expected albeit one that is weaker than the original in every aspect. The whole setup is pretty ludicrous and then you have small details which niggle (the inexperienced police joining the climbers, dragging a traumatised woman back down there, moaning she's sedated and then questioning her seconds later!) and as you say some of the acting is pretty unconvincing. The plotting is fairly second rate and predictable, as are the new characters, but the excellent photography, Shauna Macdonald and some neat set pieces keep it a cut above most horror sequels. The part where the newbies have to swing across the chasm was particularly good.
Still, the only jump was at the beginning when Sarah first appears. That really got me! And that brings me on to the ending...