This book is impressive.
It is over 100 years old and works, in many parts, like a mixture of a war report and the diary of a Victorian explorer out in the wilderness. The descriptions both of the Martians and their technical devices is amazingly detailed.
The titel, though, is a bit misleading, I feel: There is no actual war between extraterrestrial invaders and humans defending Earth. Humankind (or, more specific, Englishmen) get into a few short skirmishes before being overrun by the superior machinery of the aggressors. Also, as far as the narrator knows, there is no underground resistance forming below London. In the end, humankind is saved by bacteria which the Martians have not been prepared for. In that, they share the fate of some of the South American indigenous tribes faced with Spanish germs.
The book is, as said, over 100 years old - but still many thoughts seem surprisingly modern, such as the conclusion of the narrator that humankind must have learnt to treat other, lower creatures (i.e. animals) in kinder way after the experience of Martian "human-hunting" and what would have developed from that had the invasion been successful. These undertones as well as the stories of some of the people the narrator meets serve to balance the rather positive picture of humankind painted in contrast to the Martians.
Even though all seems well in the end, the narrator isn't convinced: He still can't forget and feels that the threat from outer space is hardly gone.