I just saw this and I had extraordinarily low expectations, but I actually enjoyed it a lot more than I thought it would.
I thought the "Scarier than Hostel!" bit that they were using to promote it was corny and dumb, because a lot of people, including me, hated Hostel. But Turistas is better viewed when you're not expecting it to be that great. There were a few parts I thought were somewhat dumb, but the acting isn't bad. All of the actors are in their late 20's to early 30's, which I thought was good because I did NOT want to see another dumb teen-driven horror flick. But I don't see Turistas as a horror movie. It was a thriller that was actually somewhat scary, which is something that suspense movies these days lack terribly.
The parts I didn't like about it were overlookable. Like in the underwater scenes, I thought the acting could have been a little better, but in the long run, Turistas isn't a failure. I think there are much worse movies that could be on the Bottom 100, like Lady In The Water, for example. So, if Turistas is showing now at a 2nd-run house near you, you should go see it. Hopefully you won't hate it as much as typical IMDb folk do. They're all idiots, anyway.