The 5th Lost Fleet book is coming out _next_week_! *bounce!* Hopefully Audible will get it in stock at the same time.
I used to think all military SF was kinda dumb, but in the last several years i've gotten sucked into several such series. (I think the Vorkosigan Saga may actually have been the gateway drug =) Unfortunately i'm not sure what's particular about the series i like and the ones that i still think are dumb. Which makes it hard to find new ones.
The ones i do like so far are Weber's Honor Harrington series, and his Safehold series, though that is a _little_ less military focused, Weber and Ringo's Prince Roger series (which has the added benefit of also having a strong element of the "relatively high tech people stranded in a relatively low tech environment" theme that i really like, which come to think of it is also one of the strong points of the Safehold series as well,) and obviously Hemry/Campbell's Lost Fleet series (which has a pretty weak initial setup, but gets better after that.)