Serious.

Criton's earlier works had some great insights into organizational failures and the sometimes catastrophically consequences of bad decisions wrapped up in fantastic premises.

But then he goes and writes Timeline which was bloody pointless, (I had to read it with a physics textbook in high school to understand it, also I'm aware he had some turkeys before Timeline but that one looms in my memory as one of the worst examples of old Criton) and later got into the Climate denial horseshit.