I finished Slan, by van Vogt. I enjoyed it. It's not without flaws - this is van Vogt after all - but it charges along and this very pace helps you from inquiring too deeply how well it all fits together. No sooner do you read a highly fortuitous plot device or some hand-waving technological description and start to think, "Hey, now, wait a minute..." than van Vogt sweeps you off again with the next improbable development and you kind forget the issue you had. Having finished I'm not sure how well it all holds together or not, but I'm not sure I care overly. This was the most popular (or well-regarded) SF novel of the 1940's, probably, so if you're a student of SF literature, I'd recommend giving it a go. "Fans are Slans"!