There’s a review of it in The Times. I remember reading his 2002 biography of Lenin with great interest, and I haven’t had a chance to read his Stalin biography (never had much interest in Stalin actually). In any case, an anecdote: Trotsky liked to hang out in Cafe Central in Vienna (as I have learned recently) and apparently when the Austrian Ministry of Interior received a request from Russia to squash the revolutionary activities in Viennese cafes, the minister reacted with laughter asking: “Who do they think will make a revolution? Herr Trotsky from Cafe Central?” Herr Trotsky, of course, did go and make a revolution later on and The Times has a nice picture of him and Lenin:
Perverse Egalitarianism 
It’s not a very honest book, full of errors and obvious that Service has read very little of Trotsky’s enormous collected works. He openly stated his unscholarly intentions with when he said “If the ice pick didn’t finish him off, I hope my book does.”
Even Deutscher’s glowing account or Trotsky’s own autobiography “My Life” is more balanced. A much better critical account of Trotsky’s life is the one by Volkogonov.