1) A Study in Pink: Razor-sharp, fresh, magnetic, and the beginning of a beautiful friendship that is persuasive and moving from the first minute.
2) The Reichenbach Fall: The wonderful response to A Study in Pink that wraps Seasons 1 and 2 in a very satisfying story arc--that of Sherlock's humanization.
3) A Scandal in Belgravia: Lovely, evocative, with the best music score and some of the most poignant moments of the series.
4) The Hounds of Baskerville: Some of the best moments between Sherlock and John, their last days of happiness together.
5) The Empty Hearse: Much better on a rewatch, utterly whimsical but enjoyable, with nice inside jokes.
6) The Great Game: Some of the cases were a bit of a stretch, but the final face-off scene makes it all worth it.
7) His Last Vow: The first thirty minutes were very enjoyable and convincing. Then the episode sails off to sentimental land--and I just feel betrayed by John Watson and the whole show in the end. However, Cumberbatch delivers some of his best acting.
8) The Blind Banker: CSI London, clichéd.
9) The Sign of Three: Puerile, corny and embarrassing to watch.