I agree with you regarding the first half of Hostel. I started to wonder where the horror element of the film was as it was quite slow and boring. The only good part is the last section from the torture chamber scenes onwards. But I think it is worth watching for those bits alone if you are a horror fan due to the realism of most of the torture sequences.

*** warning for the squeamish here, the following paragraph is quite descriptive ***

I have to mention the girl with the eye sticking out of the socket again though as that did ruin the realism of the film a bit. It just didn't look real and did look like a false eye stuck onto her face. The yellow fluid flowing out after he cut the eye out via the stalk was quite a nice gross touch though and not a scene to watch will eating.