Triplanetary

It's cheesy. It's campy. It's so ridiculous, it makes Buck Rogers and Flash Gordon seem grounded. However, it's also fun.

The lensmen stuff in general is the sort of early 20th century ridiculous sci-fi that used to get kids to read in bed with a flashlight.

Not really a fan, but it's far from the worst early 20th century sci-fi I've read. If this book were a film, it'd be Ed Wood rather than Dino DeLaurentis.

This is really a "prequel" written somewhat later, but in internal chronology it is the first in the Lensman series, and fills in some background. We are introduced to the benevolent Arisians, who are responsible for all life in this universe through a kind of panspermia. Then the evil Eddorians come in from another universe looking for worlds to rule, and the battle of the millennia ensues. The human race is one of the "Arisian" races, and the plan involves a breeding program over centuries leading up to something, and this book tells some of that story.

I read this as part of a collection "The Works of E.E. "Doc" Smith"

Although it feels dated in some aspects, it is one of the great classics and a must read for any sci-fi fan.