The characters are clichés--there is a married, responsible woman; a slutty party girl; an unsure bride-to-be; and a man-hater who just got dumped. The hitchhiker is genuinely nice until he goes crazy.
There's not nearly enough gore, and way too much rape. I enjoy slasher horror/thrillers a lot, and this one did nothing for me. The ending was just as lame as the rest of the movie.
On the positive side, the actors did a great job with that they had to work with. The dialogue isn't awful, and overall I was impressed with the cast, having never seen or heard of any of them before. And the plot wasn't out of the realm of possibility (although I really doubt any woman in this day and age would pick up a hitchhiker--no matter how attractive he is), so I wasn't groaning that things didn't make sense.
Overall, "The Hitchhiker" was well-acted and made sense, but wasn't very interesting. There are a lot of better movies in the same genre that I would recommend over this one ("Rest Stop," "The Devil's Rejects," "Texas Chainsaw Massacre," even "The Hitcher" remake). Do yourself a favor and skip it unless you don't have any other options.