I'll tell you why people hate this movie...*spoilers*
There's a certain point where you have to say, "COME ON! HOW STUPID ARE WE SUPPOSED TO BE?"
One reason people may hate this movie is the fact that no one can find a random animal in the northern woods within a week, let alone about 2 hrs. After he left his dying wife back with the other infected townspeople the character played by Hoffman then goes out to sea, gets on a ship/boat (whatever for whoever wants to get technical) and locates the picture of the animal/host. Then within, lets assume another hour, he then flies to somewhere in Massachusetts to capture the monkey. Then, he flies from Massachusetts all the way back to California within an hour to two and within that time he concocts a miracle science experiment to cure the townspeople who are infected. Now, let me ask one thing: It seemed that most of the people in this movie with this virus died within about a day or 2, not 3 days by a long shot. It was a fast moving virus that incapacitated people that even breathed it in, in only a couple of hours (if that). Now how in the world, seriously, was his wife still alive by the time he even returned??? Notice how fast the virus worked on their lab friend (Spacey)?
I think it's simple why a lot of people didn't like this movie: It's just impossibly realistic. His wife wouldn't have been alive that long, he couldn't have made a cure in a few mins, and there's no way that the town wouldn't have been bombed and covered up and Hoffman's character NOT killed after all the orders issued. And I know 95% of all movies are meant to be completely far fetched, but this one warrants an eye roll.
Now, after all that was said, I actually liked this movie LOL. No joke, I'm not even being sarcastic, I really did like it. The tone of it reminds me of Dante's Peak a lot, another long shot movie, but more realistic than this lol.
Before anyone says it, I KNOW it's fiction and it's meant to be unrealistic to a certain degree, but no one watched this and expected some ridiculous haphazard plot to ensue either. I'm just responding to those who are clueless as to why a lot of people didn't like this film.