1. I don't like GIU so much and there are two reasons why.
2-1 too many drills
2-2 not aimed exclusively for Japanese learners
(3 experience in NY) ...not enough time to write...
In the previous entry, I wrote that I don't know whey so may learners of English in Japan recommend grammar in use, but I've not mentioned my view whey I don't like it nor gave other textbooks I can recommend in exchange for that. Now I'm going to show you two reasons why I'd rather do without using that one.
Firstly, I don't believe in drills. Drills play an indispensable role of education in Japan from elementary schools to high schools, but I don't think drills can enhance your memories or activate learning. I understand drills are there thoroughly for teachers, not for students to learn. As for the GIU, the half of the book is spared for the drills, but I doubt that much of drills is truly necessary and useful to learn English grammar, especially for those people who do tadoku and tachou continuously. You will come to learn lots of basic rules of English grammar without knowing it during reading, so minimum amount of drills is what tadokers really needed to tackle with to be able to use grammatically correct English.
Also, there is a big lack of element for those textbooks which are written in English and aimed for people who are natives of various kinds of languages. There are some particular aspects of English grammar which only Japanese speakers mgiht find them difficult to master because some English concept such as perfect tense simply doesn't exist in Japanese. Those pitfalls we Japanese learners are likely to step on are different from the ones others learners who don't speak Japanese. Thus, we don't need to learn a lot what we can understand easily. Just a bit of explanation will let us realize those rules are used in the sentences you've encountered while you're reading books and you'll grasp the rules at once. What you really need to spend enough time to learn is those pitfalls that only Japanese are apt to fall in.
I think GIU is one of the best textbooks at the moment. However, if you're likely to be overwhelmed with the amount of drills, then it might not that bad to try to find another one and I'm sure you'll run into some best for you once in a while if you're truly curious and eager to master English.