Here's what worked:
1. Watson asking Sherlock to be his best man. My favorite scene in the episode, even better than Sherlock's speech. Have blinks ever been so hilarious as when Sherlock finally realizes John is saying he's his best friend? "Of course you are," says Watson.
2. The speech: Particularly this bit, worth printing nearly in full: "The point I'm trying to make is that I am the most unpleasant, rude, ignorant, and all-around obnoxious asshole that anyone could possibly have the misfortune to meet. I am dismissive of the virtuous, unaware of the beautiful, and uncomprehending in the face of the unhappy. So if I didn't understand I was being asked to be best man, it is because I never expected to be anyone's best friend. Certainly not the best friend to the bravest and kindest and wisest human being I have ever had the good fortune of knowing. John, I am a ridiculous man. Redeemed only by the warmth and constancy of your friendship. But as I'm apparently your best friend, I cannot congratulate you on your choice of companion. Actually, now I can. Mary, when I say you deserve this man, it is the highest compliment of which I am capable ... I know I speak for Mary as well when I say we will never let you down, and we have a lifetime ahead to prove that." Is it just me or does Benedict, all dressed up in that nice suit with his hair all neat, look a tad like ... like ... don't hit me ... Joel Osteen? I realize that's not a flattering comparison, but Osteen is like Benedict's older less-attractive Texas cousin.
3. Sherlock as a bridesmaid's wingman. "Mr. Holmes, you're going to be incredibly useful ... can I keep you?" Indeed! If only we could all have our own Sherlocks for everyday purposes. Just imagine having Sherlock Holmes accompany you to the auto mechanic and asking your boss for a raise. So much would be easier with a Sherlock. Mary benefits from this too, asking him cheerfully, "Who else hates me?" as he hands her a prepared list.
4. There's something about Mary. Only two episodes in and Watson's partner has effectively broken up the boys' club without seeming like a buzz-kill. "Neither of us were the first."
5. Drunk-lock! The stag night sequence shouldn't have worked -- it's long, it's surreal, it makes a joke of the show's usual whole investigative process (more on that later). Yet, again, it's so entertaining you run along with it, complete with a dubstep Sherlock theme. Particularly liked the Sticky Head Game and Sherlock's usual on-screen text analysis being drunk-garbled. "The game is ... something..." And yes John, you are a pretty lady.
Also: This Redbeard that Mycroft mentioned. Some obsessive fan analysis about that here.
7. Inside Sherlock's brain: Easily the best part of tonight's crime story. Sherlock has always excelled at finding new ways to visually illustrate the detective process. This game-show-like sequence took the process of elimination and made it engaging and gives you a sense of what Sherlock's thinking without his usual yakking to Watson (plus, nice cameo from Laura Pulver). Notice who lords over Sherlock's mental chamber, who bosses him around and commands his thoughts? Mycroft, which is perfect. (Fans on Twitter called this Sherlock's famous Mind Palace but I don't think it's the same thing -- that's more like a device for visualizing memorized information).
8. Sherlock revealing Mary's pregnancy.
9. That telegram hint. One of the telegrams read by Sherlock was from "Cam" and disturbed Mary. "To Mary, lots of love poppet, oodles of love and heaps of good wishes, from Cam. Wish your family could have seen this." CAM = Charles Augustus Magnussen -- this season's new big bad, who we glimpsed at the end of the the first episode. Though ... we keep calling him a "big bad," but since we don't really see him in at least two of the three episodes, how big can he really be? And seeing Mary's unease suggest she's hiding something in relation to this year's villain.
NEXT: What did not work