If not thinking that they made a worst mistake ever - brining wraith to Earth it was pretty good episode. The way it started - I thought as the start promised, to be lovely try to solve the code episode but what came out - it was really... exciting. The kidnap, McKay and his sister all together dealing with the nanos and dying kid... A lot of excitement, specially the end.
On the writing, I think it was not the best episode as the story looked really chaotic and not well structured but they made it up with the excitement. And the illogic with the wraith on earth and letting man to sacrifice himself... It makes me wonder how could this would have been if those mistakes were avoided as it was great episode.