(NO SPOILERS) After the beginning of the movie where everything is being introduced, the action starts and doesn't stop till the end. The constant suspense and thriller keeps you hooked. The portrayal of human emotion is not only displayed well, but the way it impacts the character's actions is accurate. One might think action A makes more sense, but human emotion might make you choose action B, the reckless one, and that's demonstrated well in the movie. IMO, most actions that happen are either reasonable or caused by human emotion, but either way none of them were entirely stupid and poorly written. Since the villain is a highly intelligent and skilled alien (the "perfect organism"), it's actions aren't impacted by feelings like other antagonists. The Xenomorph instead solely concentrates for its goal of hunting the characters, which I think makes the alien's actions better written and thrilling since there are no emotions limiting it.