It seems most obviously good names are either reserved, taken or high premium, although I have not checked all that much. For Red Sox fans green.monster would be nice but its like over $500. Porkbun show the renewal as standard though - does someone know if that is right and applies to all domains in the TLD.
It is simplistic thinking, I guess, but one thing I like to do is see how popular in search results an extension by itself is. On that grounds monster is 15x or more less popular than .best and even less compared to .top, for example.
I think a few exact match ones will find end use but don't see much for domain investors here.