Aliens of London is really very good. It has a strong and gripping plot, plenty of tension and action, a good sprinkling of humour, and some excellent character moments. The dramatic irony leading up the the cliffhanger is so well done, and the way the episode subverts expectations with its handful of twists and turns is really good. The humour in this episode may not be for everyone, but I loved it. The characters feel real and believable, and the dialogue really works to support this. Some of the effects look a little dated, but I felt that most held up really well and that the episode looked very solid.