This is a rather old book. It is similar to Courant & Hilbert's 2 volumes in content, but is more pedagogical. The style is that of a mathematician rather than a physicist - there are many theorems and proofs, and not so much solving physical problems.
This is a good addition to my mathematical knowledge, but like with Courant & Hilbert, I am glad I read it after already learning the subject from more 'practical' books!