This is a solid supplement to other German books by Herr Swick from McGraw Hill. One will neither achieve nor maintain fluency with this book alone (unless they have prodigy-level retention skills), but if you're stateside and can only use German television shows/movies, etc. to bone up on your Deutsch (plus whatever Germans you actually know) this is a good tool to keep in one's box.
I'm not sure what goes into selecting the length of each exercise, or how they determine which facets of grammar should be emphasized. If I had to guess I would say students and teachers are polled and assessed for those areas where they're weakest, and the contents of workbooks are skewed toward that. The one-size-fits-all stuff doesn't work, naturally, for everyone. Certain exercises, for instance, dragged on for a couple of pages, while others were only two or three items long. The book has "drill" in its title, so I'm not complaining that the work is repetitive and sometimes close to drudgery (nobody likes doing sit-ups but a six-pack looks good), but I was still a little confused about why some exercises were long and others were short, especially when the ones on what I considered simple topics were long and ones I needed refreshing on were cursory.
Someone in a review of the more comprehensive "Complete German Grammar" noted that the editors/authors made a handful of mistakes in the answer key there. I didn't notice it in that book (which I rated 5 stars), but I did notice it here. That said, linguists disagree on certain points of grammar or diacritics, and believe it or not there are running orthographic disputes in the Germanistik field; the continued use of the "esset," for instance or "double S" thing that looks like this ("ß") is being debated by the Keepers of the Words (or whoever decides this in a post-Brothers Grimm/Martin Luther landscape).
It's possible that there are no mistakes in the book, and that I was merely taught different by my professors for reasons I either never knew or have forgotten. Anyway, recommended, and it might not be a bad idea to work one's way through this text once per year or so to stay fresh.