i had just started up my own reading of all the TOS books about a month ago, Captain Sarine. I've been reading them in publication order. I just finished "Yesterday's Son." Loved what was there, just wish it had more meat to the story. But then, I have yet to read "Time for Yesterday." I'm holding off on reading Star Trek 2 and 3, until i get to 4. Then i'm gonna read all 3 as one big trilogy. I just started "Mutiny on the Enterprise" last night. Gotta say, it's starting off better than Vardeman's last TOS novel, "The Klingon Gambit."
Mutiny on the Enterprise was good, I thought. Interesting ideas. I agree Yesterdays Son was a bit short, and felt like more could've been explored and explained. Time for Yesterday focuses more on Zar and Spock, Kirk, and McCoy in his world. I hope that's not a spoiler. It's a longer novel, and well written.