Not sure what exactly you're saying with the "Rache" thing, it made sense to me. All Sherlock deduced on that front was that she was trying to write "Rachel", they then tried to figure out who Rachel was and, with research, learned she was the woman's deceased daughter. After that, Sherlock was trying to figure out why she would scratch her dead daughter's name in the hardwood (rather than just thinking about her) and realized it was the password to track her phone and find the killer. Seems a reasonable step in logic for Sherlock Holmes, to me.
There's so much negativity in this thread, I, for one, can't fricking wait for the new season. It's interesting that Elementary is coming up as I am currently bingeing that series (just started season 4) and I really really like it. I readily admit that there are many things it does better than Sherlock (coherent mysteries, more in-depth supporting characters, diversity) but it is a very different show, and I agree with the folks upthread, in that (apart from character names, and very broad themes) it doesn't really have much more in common with Sherlock Holmes than other procedurals named after one super-smart lead (like House). Almost all crime shows are already kind of in the mold set by ACD back in the day, but as I said, I do really like it as it is.
I still like Sherlock more, because it isn't a procedural. There's nothing wrong with procedurals, but they just have a very particular pattern that each episode follows, one that I can often guess. I like that Sherlock it is a character-based action-adventure that kind of does whatever it wants, but I can also see why some people don't like that. I just love the roller-coaster ride, though I admittedly only saw the whole thing when season 3 was airing, so I didn't have years of preconceived expectations to either meet or not.
My take away is that, while I love a good mystery, I find the overarching plot and character-work more interesting, and I think the writers do, too. I love John, I love Sherlock, I love their friendship and I love what Mary added to it in season 3. I love Mrs Hudson and her ridiculous and growing backstory. I can't wait to learn more about Sherlock's past and more about Mycroft and the Holmes brothers' fascinating relationship.
It is not at alI perfect, but I am very interested in the story Moffat and Gatiss are telling. In particular, I'm really curious about the answer to "the big question no one asked". I can't wait.
Though, I also love the Guy Ritchie films, so maybe my opinion is invalid :D