Triplanetary by E.E. “Doc” Smith - 3 out of 5.
This is the first book in the Lensman series. (Though I believe it was actually brought out after the original series as a prequel, but based on short stories written before those original books. Confused yet? Well there are also at least two versions of this book knocking about with various additions & subtractions. I have (what I think) is the longer version).
To be honest the first 6 chapters (& nearly 100 pages) are pretty superfluous to the rest of the plot. There's a bunch of historical stuff from Atlantis to Rome to the World Wars, all of which I could have done without. After this the story kicks in properly.
There are some decent aliens, space battles & weaponry on display here, alongside the usual “futuristic at the time, but old fashioned to us now” SF stuff. The writing & language style is a very old style too, the guys are all pretty macho males & the women are pretty drippy stereotypes.
An aliens race is after Iron, all Iron, the fact that some can be found in human blood is of no consequence to them. The basic story is pretty simple, but there's a lot more going on in there too. I enjoyed the twin plot lines, always works to keep me reading more. There is a decent attempt made at the different races not automatically understanding each other & learning to speak together, so often overlooked in SF. I did rather enjoy seeing a polite alien race who, after some trouble with us humans, are quite happy to treat us like bugs in a laboratory.
The ending is all rather quick & convenient. This is often compared to Asimov's Foundation Series. Well I can't see it from this first book, but maybe it builds into more with the further six novels?