Can I cut in here?
I’m actually having the opposite problem. Grammar is what made me give up Japanese two years ago and again a year ago (though I was admittedly much dumber then), while vocabulary and kanji was very easy to learn. Now, instead, I find vocabulary and kanji so boring despite not even having an N5 vocabulary. However, I have been exposed to a lot of grammar in a short period of time because of all the reading about it I’ve done. It’s fresh in my mind, because I only really started studying grammar two or three weeks ago.
The thing to keep in mind is that grammar is only hard when you’re just starting, because Japanese is full of some pretty alien grammar. Just read about grammar every day - it doesn’t matter how much you do - and eventually you’ll get a foothold on it and you’ll want to learn more, I’ll bet. I’ve found it very interesting.
I always read one of Tae Kim’s lessons from his grammar guide (not his complete guide) every day and now I’m up to special expressions. It’s been great in getting me exposed to new and common grammar structures and whatnot. I quite like it: http://www.guidetojapanese.org/learn/grammar
I’ve read through all of the 100 grammar points here, just so I can be exposed to it (the explanations aren’t so great, beware, though comments may have answers for you): http://thejapanesepage.com/grammar.htm
I also read a little of Imabi, but I’m leaving it until I finish Tae Kim’s Special Expressions because it’s a little too much content. I want to get a foothold on the grammar points first and then get more comfortable with them with Imabi’s more comprehensive (and potentially more accurate) explanations. Imabi is very comprehensive, and covers a VERY large amount of grammar, so it’s a great reference guide or supplement (maybe even a main textbook at later stages) for pretty much any level beyond absolute beginner: http://www.imabi.net
Here’s a link that gives you a rough idea of Imabi’s equivalence to the JLPT levels that you might find helpful: https://www.reddit.com/r/LearnJapanese/comments/52e8oj/imabi_jlpt_level_equivalence/
A particularly fun one that I found randomly a week ago helped a lot in both understanding and staying interested in grammar. Studying grammar concepts in a vacuum can only be so fun, after all: https://www.youtube.com/watch?v=-stbdKehONw
Game Grammar has 19 videos of LeafGreen all the way up to the first gym, and with each part about 20 minutes long, the narrator explains every grammar concept as well as the words used. I’m only 4 episodes through, but the grammar concepts started to really click for me here. Give it a shot, perhaps after you’ve already tried studying from Tae Kim’s guide or whatever.
Renshuu is another option, though I personally didn’t use it very much because I didn’t discover it until a few days ago. Unfortunately, the free version covered most of the basic stuff I already knew. It might be a good way to drill those grammar points, though. It does cover a good deal of the N3-N5 grammar from what I hear, but more than half of it is locked behind the PRO screen. You can get 30 PRO days free, though, for each person that signs up because of your referral through a particular link, like so. It might be worth it, might not. I plan on buying a month for $4 soon anyway just to try it out. You can do some stuff with the free version too, of course.
Textbooks are a great method of learning grammar, if expensive. I like An Introduction to Modern Japanese. The grammar explanations are fantastic, though it is expensive. You also have to buy the second book, which contains the exercises AND the vocab that’s used in book 1. It uses Kanji right off the bat. It’s meant as a 1-year intensive course in Japanese that will leave you with a firm grasp on the language after finishing it, as it says in its introduction. There are 52 lessons, presumably with the assumption that you absorb one lesson per week (not read one per week). I knew some of the content, so I went at a pace of 3 lessons a day. Though, I gave it a bit of a break until I finish Tae Kim, again. From what I’ve read of the first 10 lessons, it’s a fantastic book with concise grammar explanations and some content that I didn’t find anywhere else. I recommend it. The books are $60US each if you buy them, but if you rent them for about a year, it goes down to $50US each. Maybe you can rent them for like a week and see if you like them, then rent them for a longer period if you do.
Genki is usually the beginner’s textbook of choice. It’s slow and typically engaging enough, starting off with romaji over the hiragana in the first two lessons but culling it in the third lesson, I’ve heard it’s a great introduction to the language. Haven’t used much of it myself. It is the #1 best-selling book.
Minna no Nihongo starts you out reading Japanese explanations of Japanese grammar, which I thought was a rather clever idea because it gets you used to seeing Japanese in the beginning stages, which ultimately makes progression faster in the long run. It has a translation book, though, so don’t worry about not understanding it. Haven’t used it myself, but I believe it’s a series of textbooks that take you up to around N3? Then, Tobira is the (expensive) textbook of choice.
Of course, what would this list be without mentioning the Dictionary Of [Basic] [Intermediate] [Advanced] Japanese Grammar? These are widely considered to be some of the best reference books on Japanese grammar on the market because of their explanations, and they also cover a lot of content. I’ve heard the basic one covers so much that people hesitate to call it basic. But maybe that’s just the opinion of newbies. The entire series, I’ve heard, is about 70% of N1 grammar, and more than enough for confident conversation in Japan. Again, this is all hearsay, but it’s widely renowned.
I would link these last textbooks, but I have to go. Hope you find something there. The forums does have a post recommending a bunch of grammar resources as well, someone’ll probably link it. Laters.