Rating: - why BASIC ?
Sections of this book are thoroughly obsolete, where they refer to BASIC code. Remember that the text came out in 1985. Yet even then, the choice of BASIC to illustrate such matters as solving Laplace's equation in 2 dimensions was questionable. For computational problems, Fortran was then the main language. While C and Pascal could also have been used.

But perhaps Koonin was writing for a physics student completely unacquainted with any programming. In this case, BASIC as befits its name was indeed the simplest language to learn.

However, the book is still useful today for its advanced examples in physics. Treating cases like Monte Carlo methods for H2, and elliptic partial differential equations. If you are prepared to recode the algorithms.