In a genre that is literally over populated with cheap knock off Syfy- Channel style survival horror movies, you can certainly do MUCH worse than Chernobyl Diaries.
I think that the best part about this movie was the location. The abandoned living area of Pripyat was pretty creepy. This type of movie works better if you have a little bit of imagination and can project yourself as one of the characters. Even though none of this movie was shot near Chernobyl (yes I know there's some stock footage used in the movie, Im merely talking about scenes with the actors), check out pictures of the living areas of Pripyat. There's a good one on Wikipedia that is at least pretty similar looking as the location in the movie.
The whole concept of going on an extreme tour in a town that was abandoned after a nuclear disaster like Chernobyl is pretty cool. And in the realm of mutated people/zombie-like horror movies, its not all that implausible that there might be mutants/zombies like this.
The actors weren't terrible either. Yeah, many of the clichés of this genre are present. Incredibly poor judgment calls, non-existent survival instincts, etc. There's even a couple real puzzlers like the bear scene make you slap your head. But I've seen many movies where the entire cast is down right terrible. For what is was, the cast in this movie did a decent job.
Finally, one of the best things about this movie is that it WASN'T shot in the 'found footage/shaky camcorder' style. I applaud Blair Witch Project for coming up with a new sub-genre of horror, and there's been some movies that have used this technique well, but most of the time, its just annoying. I was happy to see that although the very beginning has some camcorder footage, the rest of the movie was shot rather traditionally.
If I had to pick the two biggest things that I didn't like about the movie is the lack of gore. Part of the reason I like zombie movies is for the mutated/dead/decayed look of the creatures. There are very few shots of the "monsters" in this movie. I would have preferred to see a little more gore. Also, the ending was kind of a cop out. I had the feel that the filmmakers got to a point where they were running out of money and rushed the ending. I don't want to ruin it for anyone, but it felt rushed to me.
So there ya have it. This movie isn't winning any Academy awards, there are some forehead-slappers, and the basic plot is one that's been done thousands of times. But for what it is, this is good entertainment. At the very minimum, it should keep anyone watching occupied for 90 minutes, and for horror fans who like this style of movie, it was pretty decent. A solid 7/10 in my book.