I really enjoyed Old Man's War and think you should read it. For me it was a 5* first half and a 3* second half (I liked the 2nd half but it wasn't 5* 'amazing'). Scalzi can write! He opens with excellent characterization, touching and real. This skill at bringing the POV character to life, at catching the vibe of a vital individual grown old and isolated, combines with a great plot hook. It's vivid modern almost literary writing unfolding a fascinating take on future earth. 
 The second half felt more like 60's/70's sci-fi - blasting bad guys in space. EE Doc Smith could have written it. That's by no means a bad thing. I enjoyed it. You may well too. But the transition from a very personal earth-bound story to a space romp didn't quite gell for me. 
 These minor nits aside, this is a fun, interesting, exciting, funny book. Read it. 
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