Haven’t used them myself, but I’ve seen extracts. They do seem quite well received by those of us on these forums who do use them, and most of what I’ve seen looks good. I’ll leave you to read everyone else’s experiences. I think one obvious advantage of using them is that like any other reference work, they’re probably going to be easy to find information in, which may save you some time, at least until you discover what search terms give you the best results for Japanese grammar explanations in English (or in Japanese).
However, what I will say about the more advanced levels is this: once you’re able to use online resources written in Japanese yourself – which is an ability you can acquire before you’re able to ace the N1 – you might not need the DoJG series anymore. Also, as good and detailed as they are, some of the explanations in the DoJG have left certain WK forum users confused, particularly when conditions for using an expression are mentioned, followed by a counter-example that doesn’t clearly fail the conditions. Obviously, this points to our not seeing something that we ought to, but to me, this also means the books aren’t always clear enough: I’ve bought books from top French language reference publishers meant to help careful French writers avoid common errors and understand obscure rules. They’ve never left me confused, for all the technical language they use. I don’t see why the DoJG can’t do the same for Japanese. Finally, I tend to find any advanced reference book on a language not written in that language suspect, because it’s rarely of the same quality as books written for natives of that language, but that’s just my personal bias, albeit based on experience.
I will say, however, that I own two Japanese dictionaries that frequently detail how certain structures should be used, and I find them surprisingly concise given how much information is provided. Similarly, I’ve recently acquired a very lightweight book (literally pocket-sized and just over 200 pages long) that explains things like the difference between 思う and 考える in great detail – and with historical insights – in a way I’ve never seen in any textbook or other reference book. Thus, again, once you know enough to read Japanese resources, even if you still need a dictionary to help you along, you might not need – or want – to use English resources.
Having used some of these books (yes, at the N1 level), I really wouldn’t recommend treating this series as a textbook. Only the grammar and kanji volumes are designed in a way that allows you to learn something from context even if you don’t look anything up, albeit you’ll definitely be much better off after looking things up. The rest are clearly designed for the purpose of test prep, with a heavy focus on being knowledge repositories and providing exercises and exam tips. SKM N1 is worth doing if you’re training to pass the N1, but that’s about it.
If you’re looking for a textbook that gives you context to learn and coherent texts/recordings you can immerse yourself in, I’d recommend getting one of these instead, in ascending order of difficulty:
- Try!日本語能力試験N1: 文法から伸ばす日本語 – this is meant for test prep too, but it’s actually built like a textbook, with readings that allow you to see words being used in context. The grammar explanations are given in English and Japanese, so you can check your understanding of the Japanese against what’s said in English.
- 日本への招待/Images of Japan – this is a textbook from the University of Tokyo that’s meant for ‘advanced and pre-advanced learners’. I’d say it’s an N2-to-N1 textbook. Lots of technical terms, short translations in vocabulary lists that accompany lesson texts, and some exercises.
- 文化へのまなざし – also from the University of Tokyo. ‘Advanced learners’. It’s almost definitely harder than Images of Japan, maybe something like high-N2-to-N1.
If you want to have a look, you can use the links to the last two on Amazon here:
They’re completely in Japanese, which is fairly common for N1 materials. However, at least they stitch words and structures you’d need at the N1 level into the fabric of texts and recordings that might make learning more memorable. SKM rarely does that.