I really enjoyed the first three Underworld films and I was awaiting the fouth installment. I think the first few had a really good mix of story and action.
This film at 88 minutes is considerably shorter than the others and it was noticable when we walked out of the cinema. The plot seemed to be lacking the same substance as the other films and seemed to be based only on a scary looking child and a large Lycan ripping things apart and throwing them around.
I think that if you liked the other films you will enjoy this one good enough, however if you didnt, now is not the time to start.
The 3D worked really well, there was actually a point where I jumped when I thought something was going to hit me, this hasnt happened to me since I watched poorer quality 3D as a child.