He writes clearly and concisely, and that is somewhat unusual. He covers a wider range of subjects than most. And besides all that, he is a calvinist with other theological distinctives which I share and appreciate. It shows virtually nothing of historical theology. Good, but not very thoroughly exegetically grounded.
Exegetical theologians are hard to find.
But other than that, I don't think he has made a significant contribution. Overall, this book is enjoyable and interesting reading, and it is helpful in many ways. Grudem will strike you as a genuine and a sincere Christian who wants theology to be appreciated by all. I think it will have some general use especially among laymen and undergraduate doctrines students. Ames was powerfully influential among the Puritans and was quoted among the early American theologians more often than either Luther or Calvin.