Italics are impressions from my first read, when I did not yet know what was going to happen.
1) Hermione will be playing Bellatrix Lestrange. Oh, God! It's going to be the Ministry all over again! Was there ever a worse actress? Once again the trio are really lucky in that they just happen to have one of Bellatrix's hairs and her wand. The wand which, we are reminded, tortured Neville's parents and resulted in Sirius's death. Hang on a minute .... That can't be the same wand that tortured the Longbottoms. Bellatrix was serving a life sentence in Azkaban for that. Her own wand would have been taken and snapped in half by the Ministry.
2) No one has their own wands anymore. Dean is without a wand, and Harry, Ron and Hermione seem to be using Draco's, Peter's, and Bellatrix's. Mr Ollivander has made a new wand just for Luna. Awww ....
3) Hermione still has her Bag of Awesome. She protected it by stuffing it down her sock. Look! Socks really *are* the key to everything! This bag must be about the size of a coin purse.
4) Hermione's already taken the polyjuice. Apparently Bellatrix tastes quite bad. Polyjuice flavour accurately reflects moral character, it seems. Once again we have the issue of polyjuice only lasting and hour being completely ignored. It's not long past 6:00 AM, and Hermione has already taken the stuff. What time does Gringotts open? They only have enough polyjuice left for one person, and it seems they are squandering it.
5) Hermione: "OK, Ron, come here so I can do you." *giggle* You know you love it! This followed by Harry's "he's not my type, but he'll do," is pure 'shippy gold. Apparently Hermione has mastered the ability to disguise a person's appearance. And they haven't been doing this thus far why exactly?
6) Diagon Alley is full of beggars. These must be Muggle-borns deprived of their wands. Well, at least the Ministry isn't killing them outright. The question is, how did they get into Diagon Alley without a wand to tap the brick? Ron stuns one man who attempts to assault Bellatrix!Hermione. It seems the quality of life in the wizarding world has declined for most people under the new regime.
7) Bellatrix and co. are confined to Malfoy Manor. And it's common knowledge. Well, word would have gotten out by now, since it's been weeks. People have also apparently heard that she is without a wand. I hate this plan more and more. At least with the Ministry, they got the people they were pretending to be out of the way. The really had no idea where Bellatrix was, or if people might be expecting (or not) to see her in a given place.
8) Travers. We see interesting aspects of the typical DE attitude here which we have not seen before. He dislikes foreigners, goblins and even, apparently, gold. Well, surely being a pureblood should be enough, shouldn't it? People should just give him everything he wants without his needing to resort to something as base as money.
9) Probity Probes. Fantastic. Magical devices for detecting concealment. But I guess confunding the guards was all part of the plan. Gosh, magical security is really difficult to get around.
10) Robbing Gringotts. In all our theorising, somehow we never guessed, even when we suspected a Horcrux might be concealed in a vault, that the trio would pull a stunt like this. I knew Jo would continue to surprise us.
11) Harry uses the Imperius curse. Repeatedly. Holy shit! An Unforgivable! Gosh, who knew this stellar plan would be rumbled so quickly? Well done, you guys. Maybe if you hadn't waited *weeks* the entire wizarding world would not have known y'alls have Bellatrix's wand. But they opt to press on rather than trying to get out. So very, very ... Gryffindor.
12) "They were deeper than Harry had ever penetrated within Gringotts." Lestrange must be a *very* old family. The Black family vault was next to the one Harry visited with Hagrid in PS, which must mean that, as old as the Black name is, it's not as old as the Lestrange name.
13) The Hero's Journey. Harry has now truly entered the Underworld here, both literally and morally.
14) Gringotts really does have dragons. They train them to savagery using negative reinforcement, and keep them locked away underground in an environment clearly not suited to dragons.
15) The Lestrange vault. I want to know about all this stuff, especially the skull wearing the crown. I'm now thinking of the movie "The Man Who Would Be King", and I wonder if Jo was too when she wrote this.
16) Gemino and Flagrante curses. Griphook didn't mention that this sort of security might be a possibility? Once again, allow me to congratulate you on your brilliant plan, kids. Those two spells used in conjunction are some pretty effective security. Suddenly I feel like I'm in an Indiana Jones film, somehow.
17) The sword. They've lost it. And Griphook chose to save his own hide rather than helping them in the end. Now they're in deep shit.
18) The dragon. The trio hijack a dragon in a fit of pure Gryffindor madness, and literally break out of Gringotts. I have to wonder what Harry's future relationship with the bank will be like. Did the goblins confiscate all his gold and tell him he could bank elsewhere in future? I wouldn't be surprised.
19) Soon Voldemort will know. They've traded Gryffindor's sword for the Hufflepuff Horcrux. What of their secret helper?