First year was terrible, her educator constantly complained about her, she wasn't eating at all, a lot of days she wasn't sleeping, there were days they called us to pick her up in the middle of the day because she was inconsolable.
The moment she switched educators everything resolved -- she started eating, no more tantrums, sleeping, doing great in her activities.
Montessori is as good as the individual educators are.
Looking back I can see all the red flags -- the fact that I know about the on-and-off divorce of the first educator from her alcoholic husband tells a lot. And there were all sorts of passive-aggressive little things like "Dear parents, tomorrow will be my birthday, I will spend the time with my family and not at work, that is the way we do things here...."