It's not a rip-off of another monster. It's a movie that reinvents an old genre by showing it--and showing it well--from a different perspective. It's the best movie I've seen in theaters in a long time; I thoroughly loved it both times I saw it. People go in expecting to be explained about the monster, how it came, where it came from, all that stuff, and they're upset at the end when it's not explained. It's not meant to be explained. It's about a small group of humans caught up in this fantastic (in the most terrifying sense of the word) situation. At the core of the movie, it is a love story. The monster is just a backdrop. I loved it. I would not have it end any other way. Yes, I was surprised they didn't explain the monster at the end; but then again, that wouldn't be true to how the movie was made. Form matches function, and by seeing this unbelievable event through the eyes of a spectator, it becomes plausible and serves to suspend your feeling of disbelief.