The new episode was simply amazing, it might even be my favourite episode. There just wasn't a single part in the entire episode that trailed off it kept me entertained all the way through and all the characters in it were amazing, Rarity's melodrama, Rainbow Dash destroying the barn, Fluttershy kicking flank, and of course Twilight going insane it was all amazing.
Also it's likely overshadowed by her going insane, but showing her OCD at the start that led to it I found very good, I always did consider Twilight to suffer from OCD and how they protrayed it in several scenes was great.
Overall I can't possibly say no to that episode, all it did was make me love every single character in it even more than before. Also Celestia coming in so aggresively leading to her trolling Twilight's friends at the end was amazing. It really did make it fear for Twilight when Celestia stormed in, and that's something I didn't think would happen in such an overwise funny episode. That sudden change to serious really struck me.
I love episode 3, and it came after such an amazing 2 part Discord episode. Then Luna in episode 4? This is likely the best opening that any show series has ever had.