I read Ashes of Eden by William Shatner with the Reeves-Stevens. I really enjoyed the first part of the novel, where Kirk is coming to terms with aging and his celebrity. This felt like Shatner applying his life experience to the character -- the idea of walking into a crowded room where you don't know anyone, but everyone feels they know you. I liked the party scene where Kirk, Spock, and McCoy are huddled together, alienated from the crowd and comfortable only with one another.
Once we get into the stuff where Carol Marcus doesn't turn Kirk on anymore, but then he meets this young woman (and they keep commenting on how young she appears to be...), we start flying off into awkward wish fulfillment territory. I found the character of Androvar Drake to be pretty cartoonish, too. The Reeves-Stevens have the characterizations down pretty well, although the conflict between Chekov and Sulu seemed over-the-top. But it's not exactly trying to be a subtle book.