Something that really disturbed me was Annabelle Wallis' costume in the first season. She didn't look like she was straight out of 1919, which she should've. Her hairstyle was just wrong. That may be a spoiler, but I wouldn't really say that it is.
While I'm writing this review, filming on series 5 has officially begun and I've seen all 24 episodes that have been released thus far in a grand total of 9 days. I'm happy to say that the end to series 4 hasn't disappointed me and hasn't left me urgently wanting to know what goes on next, unlike the other finales.