Definitely one of the BEST episodes EVER on Stargate Atlantis, except that the ending sucks and was quite annoying! A dissenting faction of good replicators has made perfect doubles of McKay, Sheppard, Elizabeth Weir, Teyla and Ronon, who are human in every way and have all of their knowledge and feelings and morality, except that they have nanites in them which enable them to heal instantly. They created them in order to study ascension. However, in doing so they used up too much of their energy, and when being attacked by the other replicators they agree to let the doubles escape just before they are destroyed by the other replicators. The doubles contact their originals in Atlantis and meet on a beautiful planet with rainforests, but the other replicators have tracked their ship and start attacking the group. In order to help the originals escape, the doubles create a distraction and sacrifice themselves.
There was no need to get the duplicates killed for some stupid closure or because of limited imagination by the script writers. It would have been much more interesting to keep them alive and have them come back and stay in Atlantis for at least a few more episodes, working together with the originals like twins. Amazing episode, but very disappointing and stupid ending with such a senseless death of the doubles!