I will try to keep this as short and neutral as possible. It has been a long time since I have seen her videos so forgive me if I make a clear error here. The things that stand out the most as negatives:
- Her obsessive focus on the subject in each sentence.
- Her theory that 形容動詞 (so-called “na-adjectives”) are nouns.
- Her insistence that she is teaching Japanese “as it really is”.
- Her constant attacking of textbooks.
- Her refusal to use commonly accepted naming conventions in English (and I think in part in Japanese) could lead learners to become confused when they look at more advanced materials which use linguistic terms.
These things can all be somewhat reasonably defended in the following ways:
- English speaking beginners get very confused if they don’t know where the subject of a sentence went.
- 形容動詞 are certainly noun-like and going into a detailed explanation of her disagreement with Japanese school grammar would become too confusing for beginners so it is easier to leave out the detail.
- She probably really did believe that her personal way of looking Japanese grammar was the best and was “real”.
- Textbooks do have problems.
- It is easier for some learners to understand things in the terms she created than using the commonly accepted terms.
I personally found some of these negatives to outweigh the possible methods of defending them but for some people her way of explaining things really does help and as a beginner learning Japanese you should take any help you can get.
I think for some people the issue with Cure Dolly is not her actual way of looking at things but that as she is rather evangelical it can lead to a minority of her followers having quite strong opinions about things a bit too soon in their learning journey. There are plenty of live arguments in Japanese linguistics so this isn’t to say Cure Dolly is 100% wrong or anything but just that these things are lot stickier than they may appear from her videos and the fact that other textbooks/guides don’t mention them or choose a different pedagogical approach (i.e., not focusing so heavily on the subject) is a deliberate and well-informed choice (normally) and not random.
For anyone looking for something similar to Cure Dolly (approaching basic grammar from a different angle and a strong focus on the grammatical subject) then I would recommend Jay Rubin’s book, Making Sense of Japanese. Cure Dolly notes that she owes some of her ideas to him. I personally found that book quite fun.