I love how they made it a Victorian special while keeping it NOT a Victorian special. I love the meta, the fact that it was kind of a Sherlock Holmes lampoon while still managing to be a serious episode. The fact that it continued Sherlock, but only for five-ten minutes, over a whole 90 minute episode. Really, it was a great episode.
It's also nice to be reminded why I like the show. In truth, I had completely forgotten - it's so long between appearances, that the fandom can't maintain the excitement for me, and I can't actually recall all the little things that make me love the series. So, it's nice to have a refresher. Once again, though, as soon as I get a glimpse of the love between the characters and how it's so subtlely woven into the actors performances, I'm like "damn, I have emotions about this."
Anyway, it was very fun... and though I always get sad when Sherlock uses, I thought it was a very clever way to have a Victorian special/lampoon of themselves. The very brief blurry flashback to young Sherlock and Mycroft was pretty heartbreaking though. It gives me all sorts of Holmes brothers feelings. ETA: Also, the fact that Victorian!Watson interrogating Sherlock about his love-life was actually Sherlock's own head interrogating him about his love life is a BRILLIANT thing to pick apart. Especially since Victorian!Watson was fairly gender-nonspecific, beyond mentioning Irene. It also is fairly reminicent of my fic The Switches, which I thought was pretty cool - though in that fic the conversation is real, it's the answer that's a dream.
The end was great, with the way that they comment on Sherlock Holmes as a literary figure too. Gives me all the Sherlock Holmes feels.
So, very short quick reaction, I know. If there's anything in particular you want to discuss, please do so in comments! :)
Mostly, this makes me want Series 4, because I'm kinda of itching to revisit my Unfortunate Brother fic series.