Never mind the recasting. Yes, the choices seem a little odd considering the characterisations of Brooke and Emma from seasons 1 and 2, but they're actors; it's literally their job to portray different characters under direction and have it be believable. I'm a Doctor Who fan, so I'm well used to having different faces come in to reprise old characters.
It's the writing and direction that really sunk the show with season 3. Before this, there might've been a scene or two that required a little more suspension of disbelief, but the writing was usually very good and the direction gave us some very sympathetic, relatable characters, despite their extraordinary circumstances. Not so in season 3. I don't know what the hell this new "creative vision" is but I feel like there isn't one. The writing is ridiculous bordering on satire, and it feels like the actors are reading the lines cold with their least believable inflections possible. The shots feel stale and lack focus.
Wouldn't you know it? After I griped about all these things, I went to see who had been doing the direction, writing, and cinematography, and all three had been replaced for season 3. I feel ashamed on their behalf that they had a transition be THIS obvious and bad to even a non-industry viewer.