Instructive examples of elegant, clear, rigorous, terse, but "non-dull" mathematical prose
Solution 1:
I nominate Halmos. All of his writing is good, but you might look in particular at "Finite dimensional vector spaces".
Solution 2:
Pick up an issue of SIAM Review. I admit that I haven't read every article in every issue of late, but I cannot recall an article with less than "very good" writing, and most are excellent.
Solution 3:
There is a book by Bott and Tu called 'Differential forms in algebraic topology' which I think satisfies your criteria. In particular, you say it should be engaging and that is what I remember most about when I first read this book.