How was Crucible? I haven't read any TOS by DRGIII yet.
If you don't mind that the books aren't in continuity with the rest of the Marcokradiverse novels, they're good reads that show George has a strong grasp of TOS.
If you're looking for something to give you insight into the characters you see in other books, give them a pass.
Or if minor canon contradictions are a deal breaker. I haven't read them yet (they're on my shelf, waiting!) but I remember when the last movie was released, and we were discussing the versions of George Kirk in Treklit, DRGIII saying that his version was never in Starfleet.