To me, the season finale was entertaining while I was watching it, but the more I think about it now that it's come and gone, the more my reaction is "wow, fuck this show".
Holmes shooting CAM in the face: That'd have been an OK way to end it if this was the final series. A rather massive deviation from canon (Holmes taking no steps to ensure CAM's murderer gets caught is pretty different from him doing the killing himself), but whatever: the show could have concluded with Sherlock finally snapping, proving himself to indeed not only be a sociopath but a *dangerous* one that is a menace to society, and going to prison.
As this is not going to happen, though, the writers are in a bit of a bind now: there's no way they can go on from here that is not, in one way or another, despicable. Ep 1 of the next series will be about Sherlock being brought back to London to face off with (faux?) Moriarty: OK, fine, extreme circumstances call for extreme measures, blah blah blah. What then? He's still a murderer. He shot an unarmed man in the head, right in front of the police. It was not in self-defence, he was not under duress. He was just really pissed.
After the immediate threat has passed, what will happen then? Will the show continue in prison (or with Sherlock facing his de-facto death sentence undercover in Eastern Europe), or will he be pardoned in light of the services he'll render the crown in the coming episode? How disgustingly Nietzschean. "Oh, never mind that thing where you shot a guy in the head, you've been a good boy since, and he was a real prick anyway. Let bygones be bygones. And vigilante justice is actually pretty cool, saves the police work."
Mary shooting Sherlock, and her being forgiven for it, was equally harebrained. "Oh, I know you shot my best friend in the chest, but you only did so because you love me!" - give me a fucking break. John's bold declarations that he does not care about her past: if her past has molded her into a person that's willing to shoot an (at this point) innocent person in the chest (fuck that whole "non-lethally" bullshit) to avoid facing the consequences of her (actual) crimes, you'd better fucking care, you complete and utter moron.
Moffat did this on DW already, and he's doing it here too: have characters do things that seem irredeemable, and then bend over backwards trying to show how the character in question is, actually, redeemable. And fail. To hell with that. If you don't want your characters to be irredeemable, stop having them shoot people.
So, for me the show crossed a line with this last episode - it's obviously in a place (that DW has been at for some time) where Moffat cares more about shocking the audience than he cares about telling a coherent story.
Hence: Wow, fuck this show.