Man, I loved this movie!
I just saw it and I can't get why people seam to hate it. First of all, it was made in the 70's and for that it was really well done (even if the science was a little wrong, but they didn't know that then). I didn't want it to end. I just wish there were more movies like this with the animals turning against man.
I did find the ending a little to easy. I would have preferred it ending with them finding a car and driving away from town with no idea how the rest of the world looked and leaving it there.